Master of the games
From A Wiki of Ice and Fire
A master of the games is the official who enrolls participants and selects pairings for jousting matches at tourneys.
Whever he took part in tourneys, Ser Uthor Underleaf would bribe the master of the games to get paired up so that he would face the opponents he preferred—big men, older champions past their prime, and "village heroes"—where the odds would appear to be against him.
During the Tourney at Ashford Meadow, the position was occupied by Plummer, the steward for Lord Ashford.
During the Whitewalls tourney, the position was occupied by Cosgrove, the steward for Lord Ambrose Butterwell.