A game has a scoring system where players earn points. The game needs a feature to evenly distribute bonus points among players and also determine any remaining points that can't be evenly distributed. Which arithmetic operator is essential to determine the number of leftover points? 

In this scenario, the modulus operator (%) is essential. When dividing the bonus points by the number of players, the modulus operator gives the remainder, which represents the number of leftover points that can't be evenly distributed among the players. This allows the game to allocate bonus points fairly and determine if there are any undistributed points.