Green Monster

The Yankees versus the Red Sox. What a classic matchup.
The big green monster was messing with left fielders tonight, too.
What? No… no, they were playing in Yankee stadium, not Fenway.
Oh, I’m talking about an actual big green monster. It was from outer space or some science lab.
Thing showed up, dropped over the fence, and started messing with the left fielder.
Cops tried to shoo it towards the dugout, but it messed with the cops, too.
Nobody messes with New York cops. They shot the crap out of it.
I think it’s in the hot dogs.
Mustard?