Ryan is watching a football game on tv and is easily able to recognize the players as members of their respective teams, regardless of their positions on the field.
what gestalt principle is most responsible for this ability?

The correct answer is: Similarity.

Explanation:

The gestalt principle of similarity can be understood as the ability that individuals have to create relationships between objects and elements of a determined context.

For instance, in a football match the ability that let individuals acknowledge which players are from the same team is the principle of similarity; the players may share similar playing style, similar uniforms, values, etc.

So without really knowing a particular player's position on the field, thanks to the Gestalt's principle of similarity Ryan is easily able to recognize the players as members of their respective teams.