Looks like something got caught between the ball and the hitch. Between the weight on the ball from the trailer hitch and the turning motions, it would not have to be very big, even a stray pebble or some other foreign object. I would inspect the trailer hitch for damage. The damage on the ball looks cosmetic from the photo, but if you have any doubts, replace the ball for your own piece of mind.
Charlie & Lizzie the Mini Dachshunds
2008 Jayco Eagle Super Lite 30.5 RLS
2006 F250 XLT Xtra Cab Long Bed 6.0 Diesel
24 hours in a day, 24 beers in a case. Coincidence? I think not.