The Impact Engine, introduced in FIFA 12, simulated physical collisions between players.
Electronic Arts designed the system to calculate contact between footballers more dynamically than the largely animation-driven collision behavior in earlier FIFA games. Players could stumble, fall and react to challenges in ways that depended on the angle and force of contact.
FIFA 12 was released in 2011 and promoted the Impact Engine as one of its principal innovations. The technology was intended to make tackles and physical contests feel less predetermined, although early players also noticed occasional unrealistic or humorous collision outcomes.
The Impact Engine is not the same thing as the Ignite engine used for broader graphical and gameplay improvements in later releases. “Engine” can refer to different layers of a sports game, so the specific answer here is the collision system’s name: Impact Engine.