A participle is a word formed from a verb.
Like going, gone, being, or been.
It can also be an adjective like working woman, burned toast. (A verb being used as an adjective).
A verb is an essential part of a sentence structure that is referred also as the action word. In this case, the action word present here is had. The nouns in this sentence are players, guards and injury rate. The subject are the guards since they are the center of the sentence. Answer is had.