Having some bigger equipment I'd say too much throttle. I was roading my 12 row mounted planter north on saturday and took a corner too fast things seemed fine and I gave it some throttle and it got a bit loose and almost ditched it.That looks to be a bridge I bet he hooked something and it went bad pretty fast after that.Another no no is not locking your brakes together been there done that. It will scare the crap out of you.