How does the word athelete function in the sentence?

If your sentence is "Coaches consider him the best athlete in his division", then the answer is objective complement.

Explanation:

'Him' is the direct object of the verb 'consider'. The word athlete says something about this object; therefore, it functions as an objective complement.

An objective complement is a noun or an adjective which follows the direct object renaming it. In this case, it is the noun athlete renaming the direct object him.