Putting the tongue weight of a pontoon trailer on an ATV will certainly leave the front end light and make the rears dig in. Most of the Polaris atv's have a towing capacity of about 1200lb. I don't know the rated tongue weight but I'd bet that it's 300 or less. You probably had the fronts spinning along with the rears.

“In a time of deceit telling the truth is a revolutionary act.”
― George Orwell

It's not over when you lose. It's over when you quit.