Random Riddle: The Green Monster

Four legs have I, a sturdy fellow
A fuzzy back that isn’t yellow
But (often) green or (rarely) red
A den is where I make my bed
My keepers feed me colored balls
With sticks, they store on my den walls
Sometimes I store them in my pouch
Sometimes deep in my belly; ouch!
That’s when you’ll see me acting strange
Instead of balls, I’ll eat your change
And that’s my cue to feed again
Chalk it up to hunger, friend!
 
Random Riddle: The Green Monster