Last week I wrote about Hank Aaron, who recently celebrated the 40th anniversary of his record-breaking 715th home run. I concluded that Aaron would still have been a great player — and would very likely have made the Baseball Hall of Fame — even if all of his home runs had been counted as singles instead.Or at least — that’s almost what I wrote. What I actually wrote left a lot of room for interpretation (emphasis added from original):What if Aaron had never hit a home run? What if those 755 round-trippers had fallen for base hits instead? (If we’re trying to isolate the effect of his power, that seems like the fairer way to do it, instead of turning them into popups or something.) Would he still be a Hall of Famer?If all of his homers had been singles, Aaron would still have his 3,771 hits.The ambiguity is over the means by which we’re turning Aaron’s home runs into singles. When writing the original post, I’d imagined that this was accomplished by some sort of accounting trick. After Aaron retired, some Evil Commissioner decreed that all of Aaron’s homers would be counted as singles in baseball’s record book (like how the NCAA sometimes retroactively forfeits a team’s wins after it’s determined to have used an ineligible player); but it wouldn’t have changed what happened on the field.But what if the change had occurred on the field instead? So as not to violate any laws of physics, we can imagine it happened by means of a ground rule. Before Aaron made his major league debut, our Evil Commissioner decreed that any ball hit over the fence in fair territory by Henry Louis Aaron would be counted as a single rather than a home run. This rule applied to Hank Aaron and only to Hank Aaron. Everybody knew about the rule, including Hank Aaron, the pitchers who faced Hank Aaron, and the teams who employed Hank Aaron, and they were free to adjust their strategies accordingly.1A couple of complications: First, is Aaron allowed to hit inside-the-park home runs? Sure, let’s let him; he hit only one during the course of his career anyway.Next, what happens to the baserunners when Aaron hits a ground-rule single? Do they advance only one base? This would make Hank Aaron’s ground-rule singles less valuable than regular singles, since baserunners sometimes advance from first to third or score from second on a base hit. So let’s imagine that our Evil Commissioner decrees that a set of Strat-O-Matic dice shall be thrown by the umpires when Hank Aaron hits a ground-rule single. The baserunners will then be allowed to take an extra base in accordance with league-wide averages for runner advancement.This thought experiment is starting to get a bit complicated. Still, it gets to the point that the economists Scott Sumner and Tyler Cowen have made, which is that changing the ground rules for Aaron would have changed the way he and the pitchers who faced him approached the game. It thereby might have affected the rest of Aaron’s batting line and not just his home runs. There are several such effects to consider.Aaron would have drawn fewer walksThe number of walks drawn by a hitter is partly a function of his plate discipline and partly a matter of how much the pitcher fears him. The reason to risk walking a hitter, as Cowen notes, should be largely a function of his extra-base power. There’s not much reason to pitch around a singles hitter and give him a free pass to first base when most of the time the best he’s going to do is get to first base anyway by means of a base hit.This is clearest in the case of intentional walks.2Or at least it should be obvious in theory; whether it’s quite so obvious to pitchers and managers is another question. I was surprised to discover that singles hitters like Ichiro Suzuki and Wade Boggs each led their league in intentional walks multiple times during the course of their careers. Some of these intentional walks may have been prudent if first base was open and there were runners in scoring position. But I’d guess that many of them were not very smart. Still, the aggregate trend is suggestive of rational behavior. In the 2013 season, the correlation between a hitter’s rate of intentional walks drawn and his isolated power was .44. The correlation between intentional walks and his rate of singles per at-bat was essentially zero (.03).Aaron’s unintentional walks would probably also have declined if he weren’t allowed to hit home runs. According to data compiled by Fangraphs, the percentage of pitches thrown in the strike zone to major league hitters varies between about 40 percent and 55 percent. The hitters on the low end of the range are power hitters (Ryan Howard, Prince Fielder, Vladimir Guerrero, Pablo Sandoval); those at the top end are singles hitters (David Eckstein, Jason Kendall, Chone Figgins, Juan Pierre). A homerless Hank Aaron would have seen considerably more strikes.Aaron would have hit for a higher batting averageSeeing more pitches in the strike zone would have made it easier for Aaron to make contact. From 2009 to 2013, the league batting average for at-bats that concluded on a pitch thrown within the strike zone was .291; for pitches outside the strike zone, it was just .175.3Players were also 3.6 times more likely to hit home runs on at-bats that concluded on pitches thrown in the strike zone, although that doesn’t help Homerless Hank. (This research was provided to me by Mark Simon of ESPN Stats & Info.)A quick calculation from these figures shows that if Aaron finished an additional 10 percent of his at-bats on pitches thrown inside the strike zone, he’d boost his career batting average by 12 points (from .305 to .317). However, that’s a crude estimate. We’d also have to consider how Aaron and the pitchers and defenses who faced him would have changed their whole approach to the at-bat.There’s reason to think that Aaron would have adapted to these conditions more readily than his opponents. He was a smart and versatile hitter; Sports Illustrated’s 1958 scouting report described how Aaron was very difficult to defend because he could hit to all fields and leg out infield hits (emphasis added from original):Man who excites the experts is Henry Aaron, of the loose, free swing. Called “best wrist hitter in baseball,” he’s actually an arm hitter, lashing pitch with masterful coordination of forearms, biceps, wrists and bat. Slumped through June but has had best record in league since then. No set way to fix defenses against him, since he hits to all fields, bunts beautifully, is fast enough to beat out infield hits. He’s also a good, if lackadaisical, outfielder, with a fine arm. The team’s big man.Furthermore, we have some experimental evidence on cases in which Aaron had an incentive to hit for contact. He performed very well in these situations.Singles increase in value relative to home runs when there are runners in scoring position. For his career, Aaron hit .322 with runners in scoring position.4Aaron accomplished this by means of hitting more singles; 20.4 percent of his at-bats with runners in scoring position concluded with singles, compared to 17.6 percent with the bases empty. His rate of extra-base hits was largely unchanged. Note that there is not a strong systematic tendency for players to hit for a higher average with runners in scoring position. In 2013, major leaguers hit .255 as a group with runners in scoring position, compared to .253 for all at-bats.Singles become more valuable still when there are runners in scoring position and the score is tied late in the game. In these cases, either a single or a homer will usually score the go-ahead run and win the game, so the hitter should be hitting for contact and the pitcher should be trying to prevent contact. I looked for at-bats on Baseball-Reference.com’s Play Index when Aaron hit with runners in scoring position in the seventh inning or later of a tied game. It’s a small sample — just 139 at-bats. But Aaron hit .331 in these situations for his career.Another natural experiment comes from cases in which home runs aren’t necessarily less valuable, but are harder to hit. Of the ballparks Aaron played at regularly during his career, the one least conducive to home runs was almost certainly Forbes Field in Pittsburgh, where the left field and right field power alleys were 392 and 395 feet away from home plate, respectively. From 1954 (Aaron’s debut season) until the Pittsburgh Pirates’ last full season in Forbes Field in 1969, the Pirates hit 65 percent more home runs in road games than at Forbes Field. They also hit for a slightly higher batting average in Forbes Field than on the road, although the difference was modest (.267 versus .259).How about Hank Aaron? He adapted wonderfully to Forbes Field, hitting .338 for his career in 639 at-bats there. That’s a little bit better even than Pirates great Roberto Clemente (.329), whose game was tailor-made for Forbes Field.Aaron might have seen less playing timeThe no-homers ground rule might have made teams more reluctant to employ Aaron, especially toward the end of his career. After breaking the home run record as a member of the Atlanta Braves, Aaron played two farewell seasons as a designated hitter for the Milwaukee Brewers in 1975 and 1976. He hit just .234 and .229 during those seasons. The Brewers were terrible back then, but they might not have had much patience for Aaron if he didn’t compensate for his poor batting averages with occasional home runs.It’s also plausible that the start of Aaron’s major league career would have been delayed, but this case is more debatable. Aaron’s potential as a singles hitter would have been evident quite early. He began his professional career as a 17-year-old in the Negro Leagues, where he hit .366 in recorded at-bats as a member of the Indianapolis Clowns. Purchased by the Braves for $10,000, he then hit .336 and .362 in minor league seasons in 1952 and 1953.5Furthermore, the Braves had an opening for Aaron since they had traded the veteran outfielder Sid Gordon at the end of the 1953 season. Press accounts from the time do not seem to mention Aaron’s emergence as a motivating factor for the Braves to trade Gordon, though it may have played into their thinking.Aaron might have stolen more basesIn the comments on my original post, some readers noted that if Aaron had hit more singles, he’d have had more opportunity to steal bases. This is true — although I also have Homerless Hank drawing fewer walks and perhaps getting less playing time than the real Aaron, which would counteract his increased rate of singles.It’s probably the case, though, that Aaron could have stolen more bases if he’d wanted to. He was reasonably fast early in his career, as the Sports Illustrated scouting report mentions. But the stolen base was not in vogue in the 1950s and Aaron rarely attempted to steal. Steals became a much more popular strategy in the 1960s, however, and Aaron proved to be a proficient base-stealer. He stole 240 bases during his career and was successful on 77 percent of his steal attempts, leading the National League in stolen base percentage in 1966 and 1968. His high rate of success suggests that Aaron may have left a few opportunities on the table. Perhaps if he had been cast as a singles hitter, his teams would have expected him to be more active on the bases. He presumably also would have hit first or second in the batting order rather than third or fourth, which means he’d reach base more often with second base open.Aaron might have hit doubles and triples at a higher rateIf Aaron had only been credited with singles on balls that cleared the fence, he would have had reason to swing for the gaps more often in an effort to hit doubles and triples.In general, however, it’s not all that easy for players to try to hit doubles. The league leaders in doubles change quite a lot from year to year and the lists mostly comprise good overall hitters who play in stadiums like Fenway Park that are conductive to doubles. Still, none of those hitters faces incentives where doubles are actually more valuable than balls hit over the fence. As the scouting reports and batting splits makes clear, Aaron could hit to all fields and was smart about adapting his approach to the situation. I imagine that he’d find a way to hit a few more doubles and triples.Summing upThe real Hank Aaron hit for a .305/.374/.555 “slash line” (batting average/on-base percentage/slugging percentage). If all his home runs had been changed to singles after the fact, his line would have been .305/.374/.371 instead. But this doesn’t account for the changes Aaron and the pitchers might have made as they adapted to the ground rule.It’s just a guess, of course — but I imagine that Aaron would have hit somewhere in the .320s as a result of seeing more strikes and changing his approach to make more contact. His slugging average would have gone up accordingly, perhaps also boosted by a few extra doubles and triples. However, he would have drawn fewer walks, which could offset any gains in his on-base percentage. I envision his slash line as being something like .325/.375/.405, which is reasonably similar to Rod Carew’s.I don’t think Homerless Hank would have been in any jeopardy of failing to notch 3,000 hits. He may even have reached 4,000. The real Hank Aaron had 3,771 hits, and I have Homerless Hank hitting for a higher batting average. I also have him drawing fewer walks, which means more opportunities to put the ball in play. In fact, a .325/.375/.405 batting line would translate to roughly 4,150 hits given the number of plate appearances Aaron had. That would put him in striking distance of Ty Cobb, who had 4,189 hits. (Pete Rose surpassed Cobb’s record in 1985 and finished with 4,256 hits.)I also imagine that Homerless Hank wouldn’t have been very productive in the last couple of seasons of his career; his batting average over his final three seasons was .244. Teams don’t normally have much interest in singles hitters who hit .244. Still, they sometimes find spots for players who are pursuing career landmarks; Rose was somewhere between marginally productive and counterproductive after the age of 40, and yet he got (and gave himself as player-manager) another 2,469 plate appearances. If the Braves or the Brewers had been so generous to Aaron, it’s possible the Home Run King would have ended up as baseball’s Hit King instead.