What prevented him from participating in the game?

The correct answer indicates that a back injury was the primary reason he could not participate in the game. This choice highlights a physical condition that directly affects someone's ability to engage in an athletic event. Injuries, especially to the back, can be significant and often debilitating, making it a valid and serious reason for not taking part.

In contrast, other reasons like fear of losing, a strategy decision, or a previous commitment do not pertain to an individual's physical health or immediate capability to join the game. While these other options could certainly influence someone's decision to participate, they do not hold the same weight as a medical issue that physically restrains someone from playing. Thus, the presence of a back injury stands out as the most concrete and compelling explanation for his absence from the game.