1) Why is the left-hand police officer so late in reacting to the runner? She should have seen him in her peripheral vision running towards her with his hands in the air and reacted as he passed her. Instead she doesn’t start to react until a second after he has passed her. It’s almost as if she just sensed his presence as he passed her.
Just adding onto what's already been said, (being in the us Pacific Time Zone I'm one of the last to check in the morning), a late reaction assumes that the officer didn't see the person already. The runner comes from off camera, so it's very possible the officer has already see him/her and isn't overly interested. It's just one more kid running around for any number of reasons.
As usual with these things, we get a whole 13 seconds of "proof", so there's no before or after to establish some context. It may be that our runner becomes very obvious if the camera panned back to the left, but we don't get any of that. All we're shown is the "ghost". Conveniently.
2) The runner seems too small and slender to be a football player exercising. If he’s not a football player why is he there racing past the cheerleading team at halftime during a football match?
Not necessarily, these are high school kids. It's dark, so it's probably the Varsity game which would be seniors and juniors (15-18 years old). Back in the '80s when I was a junior on the football team (3rd string) I was a whole 5'6" and 140lbs. Without pads, that is, a team member who is injured or otherwise not playing but is still wearing his jersey, that can make one look even smaller.
And this is all assuming it's a player. deirdre pointed out a girl on the sidelines that could be our runner, and I'm leaning that way as well. Note in that picture there's at least 2 other girls that look similar to the one deirdre pointed out. Besides, there's all kinds of people on the sidelines, players, non-dressed players, cheerleaders, coaches, student assistants, officers, equipment managers, maybe some EMTs and more.
And I'll reiterate, this lady got on TV multiple times with this. Not that she used CGI to hoax it, but maybe she didn't bother to look through the rest of her footage for any clues to what she saw. Or maybe she did and decided that wasn't any fun. Just show everybody this 13 seconds and you get to be on a Halloween segment. And on a Metabunk thread!