Pooping in pants - help!

Liza

My now 4 year old has been potty trained since before he was 2. He realized the sensation of needing to go pee/poop early on. He never pooped in his underwear even through potty training. Well the past three days he’s pooped in his underwear while we are playing. He said it’s because he didn’t want to stop playing. What do I do!?!!??