My daughter started doing this around 25-26 months. I took her to the store, after forcing on a diaper, and let her pick out her own underwear. I then gave her a choice - underwear or diaper - when getting dressed. Less than a week later, she was fully potty trained! She just was done with diapers. That daughter is now 7 and enjoys hearing the story. Then there are my girl/boy twins, who are almost 3. Both are fully potty trained, and my son took the route of his older sister! What a shock, though! That boy was STRONG! I, too, would unintentionally hurt him in our battle of the diaper. I felt bad about it. I couldn't stay calm with 3 kids, and I'd almost rather cuss and yell back at that point than sing a song or make up a game. So I recalled my struggle with my oldest daughter and off we went to Target to get some undies! He was fully potty trained (even dry all night) less than 2 full days later!! Maybe your son is just really ready to not be in diapers and this is his way...like with 2 of my 3. I don't miss the fight at all. I really empathize with you!!