For a player to have a season worthy of an MVP award, many things have to go right, and for Bryce Harper in 2015, just about everything did. He set career-highs in almost every statistical category and led the league in runs, homers, OBP, slugging percentage and OPS. This was all at the age of 22.
Harper flashed greatness in his first three years in the league, but injuries beset him particularly in 2013 and 2014. In 2015 he was finally healthy for a full season and Harper believes that was the biggest key to him realizing his potential at such a young age.