I hooked a Goliath grouper a couple years ago off Marco Island. We were fishing with mid-weight tackle. At first I thought I was snagged on the bottom, butt here really isn't anything to snag on. Thing didn't move and I couldn't move it for 30 seconds.
Then it decided to do whatever the heck it wanted to. Guy I was fishing with knew what would happen. The hook would break when the fish decided it was finished. Fought it for about 10 minutes then SNAP! Buddy, who knows said it was probably a small one, 125lbs or so based on the bend in the rod.