Baseball has a complicated history with batting average. During the earliest days of the game it was the single most important stat for a hitter. Players didn't hit for power or walk much so they were defined by whether or not they got a hit. During this time starting pitchers almost never left the game, which made it a lot easier for batters. This is evidenced when we look at the top 15 all time leaders in batting average:
All those guys played forever ago. It's tougher to get a hit in today's game than ever before thanks to bullpen specialists and pitchers routinely throwing in the upper '90s.
Anyways in the early 2000's along came Moneyball, which taught us that batting average was overvalued. The case was that it could be sacrificed if a player hit for power and got on base. Some think that has now gone too far and that batting average has become undervalued. One thing we have learned for sure is that it's fluky. That's where BABIP comes into play.
Batting average on balls in play (BABIP) measures how lucky a hitter is. This stat helps explain what has happened to one of the games biggest stars this year in Bryce Harper. In 2015 Harper unanimously won the NL MVP award at just 22 years old by hitting .330/.460/.649 with 42 homers. This season those numbers have dipped to .240/.374/.441 with 24 homers. What the fuck happened?
The answer, like in most instances, is a few things. It was reported over the summer that Harper has been playing through a shoulder injury. Manager Dusty Baker has denied this but it could help explain the loss of power. Now what about that batting average? That's where BABIP comes in.
Harper has a career BABIP of .316. This stats accounts for anytime a ball is hit in play. So basically everything but homers, strikeouts, and walks. Sometimes hitters get lucky and bloop singles will fall in or they will be facing a poor defense that was unable to catch up to a ball. This will cause a player's BABIP (and therefore batting average) to rise. And unlike popular belief that luck doesn't simply "even out" over the course of a season. Perhaps this is what happened to Harper last year as his .369 BABIP was well above his .316 career norm.
So what about this year? How could his average drop 90 points from a season ago, from .330 to .240? Well, basically, as lucky as Harper was a season ago he has been equally unlucky this year. Currently his BABIP stands at .255, which of course is well below his career mark of .316. All those batted balls that were falling in for hits a season ago no longer are. Maybe he is hitting a lot of line drives right at defenders. Then again his average exit velocity is down from 91.4 mph a season ago to 89.5 mph in 2016 so he's not hitting the ball as hard this year.
So what does this all mean? Basically, Harper isn't as good as he performed a year ago when he became the youngest unanimous MVP in the history of America's pastime. But he also isn't as bad as he has been this year (which isn't even that bad it's just "bad" compared to the standard he set). He's somewhere in the middle. This may be due to him getting unlucky in the BABIP department. It may be because of the shoulder injury. It's probably a little bit of both. He's still just 23 years old (!!!) and it shouldn't shock anyone to see him approach 2015's numbers within the next couple of years.