Barry Bonds is back in baseball. The Miami Marlins announced Friday that Bonds will become their hitting coach, joining new manager Don Mattingly’s staff.1Since retiring, Bonds has worked as a spring-training guest instructor for the San Francisco Giants, but not on a full-time basis. So now we’ll get to obsessively analyze Bonds’ proportions all over again, this time in arguably the majors’ worst uniform.Bonds is a lightning rod because of his role in MLB’s steroid era, but I’m not here to re-litigate how much he cheated or what his punishment should be. The guy was pretty terrific at hitting a baseball long before we knew what BALCO was.My question is simple: Does a good hitter make for a good hitting coach?Not necessarily.To find out, I looked at every hitting coach going back to 19732The year the designated hitter was introduced. using data from Retrosheet.org, and for those who played in MLB, I gathered their Weighted Runs Created Plus (wRC+, a per-plate appearance measure of offensive production that we’re quite fond of at FiveThirtyEight) and the number of wins above replacement (WAR) that can be attributed to their offensive contributions.3For sticklers, this means I removed both positional defense and the overall position adjustment from a player’s WAR. But I did leave baserunning in offensive WAR, as is the custom for the statistic, even though that aspect of the game is often managed by instructors other than the hitting coach.But how does one go about quantifying coaching performance? It’s a complex question that I’ve struggled with over the years. One simple way to judge a hitting coach’s effectiveness is how well his hitters outperformed their expectations. To that end, I used a historical database of Marcel projections — named for the pet monkey from the show “Friends” because they’re so basic a monkey could compute them — and measured the degree to which a hitting coach’s pupils performed better in the batter’s box (according to Weighted On-Base Average, or wOBA) than they were projected to.Armed with all this information, we can see the (non-)relationship between a hitter’s offense and his coaching talents. Whether we make the comparison using the hitting coach’s career WAR, as in the chart above, or using a weighted average of his lifetime wRC+, the correlation between hitting well and coaching others to do the same is effectively nonexistent.While Bonds may have been second only to Babe Ruth among career hitters — ignoring steroids — we have no idea what that means for Giancarlo Stanton, Dee Gordon and the rest of the Marlins hitters. So while the thought of Stanton becoming even more Bonds-like has pitchers everywhere reconsidering their chosen profession, it’s still anyone’s guess whether Bonds will be able to communicate to others just what drove his preternatural plate discipline and freakishly fast reflexes at the plate.