Answer: Zero-sum game
Explanation:
Zero-sum game is defined as the strategy in which an individual or team can become a winner only if the other individual or team loses in a competitive situation.The net sum of the situation is zero in this case.This strategy is from game theories.
According to the situation, Tom and Billy's winning or losing result will create a zero sum situation .If Billy win ,Tom will lose and if Tom wins,Billy will lose.Therefore the net of their win and lose will be zero.