Bryce Harper's quick ascent to the majors could actually cost him millions of dollars in 2015, the last year of the $9.9 million big league contract he signed after he was the first player taken in the 2010 draft.
Unlike some major league contracts signed by amateurs, Harper's contract does not include a clause that would allow him to opt out of his deal if he was to become arbitration eligible before it were to expire.
Thus, Harper's salary is set at $2.25 million for 2015. Barring any unexpected minor league time next season, though, he would have accrued enough major league service time to be eligible for arbitration prior to the following season. For a player of his caliber—NL Rookie of the Year in 2012, NL All-Star in 2012-2013—he'd likely earn significantly more than his current contract stipulates.
With the 21-year-old Harper in line to eventually command an unprecedented long-term deal that would be amongst the largest in major league history, losing out on $5 million might not seem like a big deal. And $5 million probably isn't a big deal to the Washington Nationals, either, which is why they could just allow him to opt out of the deal after the season to avoid any future conflicts with their young superstar.