It's just that they take turns. The top rivals in darts, or pool, or any other turn-taking game is the same way. They have to react to what their rival left them.

> there are people on both teams who really are tackling those guys.

This is the critical distinction.

Peyton isn't deciding the defense when Brady is on offense. Brady isn't reacting to whatever Peyton left on the pool table or the dart board.