http://m.mlb.com/news/article/110016130/red-sox-agree-to-terms-with-yoan-moncada
Because he is not yet 23 years old and did not play in a Cuban professional league for at least five seasons, Moncada is subject to Major League Baseball's international signing guidelines, under which each team is allotted $700,000 and an additional bonus pool based on the team's record the previous year to be used during the international signing period. The current period started July 2 and ends on June 15.
According to those guidelines, clubs are penalized during the upcoming 2015-16 signing period if they exceed their bonus pools by certain amounts. The Red Sox had already exceeded their bonus pool before this signing and been given the maximum penalty. It's a severe measure that includes a 100-percent tax on their pool overage and prohibits them from signing any pool-eligible player for more than $300,000 during the next two signing periods. Including the penalty for exceeding their bonus pool, Moncada's deal will cost the Red Sox approximately $60 million -- the bonus plus the penalty.