Question: If Mike's ex-wife (Scarlet) recognizes him from when they were teenagers, wouldn't the coach remember him too? He was the star player.
Answer: It's also possible that the coach might have noticed a resemblance, but he would have simply written it off as an odd coincidence, much like Scarlet did earlier in the film.
Answer: I've not seen the movie, but an ex-wife would be closer to her ex-husband than a coach to his old student, no matter how good.
JonTheRandom