There are a number of things a player has to do to be a successful professional hitter. Things like, um ... seeing the ball. That would probably be at the top of the list.
It was something that Kansas City Royals first base prospect Eric Hosmer had a problem doing in 2009, which resulted in a hugely disappointing season in his first full year of pro ball after being the third overall pick in the 2008 draft. Hosmer batted just .241 with a .361 slugging percentage in 106 games of Class A ball in 2009, and poor eyesight was a big part of it. Diagnosed with astigmatism in spring training of that year, Hosmer first tried contacts, and then glasses, before finally undergoing Lasik surgery to correct the problem. Put simply, he had problems with pitch recognition, especially against left-handed pitchers. It's hard to hit what you can't see.
On top of that, Hosmer also fractured a knuckle on his right hand trying to dive for a ball, and though he tried to play through the injury, it affected his ability to grip the bat and drive the ball.
"It was stuff you can't control, but I'm just glad that's all behind me now," Hosmer said. "Some days, [the knuckle] hurt more than others, and it was just something we had to get fixed. We also had to get my eyes fixed. It's something I can put in the past and move on from."