Are things that contentious that it can't be handled through a simple conversation?
From the mom's perspective....the kid has an activity and if it's dad's night, then dad should take the kid. She drives the kid around the other 6 days a week.
From the dad's perspective...he only gets to see his kid once a week. He'd rather actually spend time with the kid than dropping him off at Cub scouts, little league, etc. and not spending any time with the kid that he loves...and misses. And it's annoying that the ex signed the kid up for all of these activities on the one and only night per week that he can spend time with his kid.
The fact of the matter is the dad has the choice of spending time with the kid or taking the kid to the activity.
Have a conversation with the ex and figure out a way to make it work...even if it means that he gets two nights this week with the kiddo....or spends Tuesday night instead.
Bring on the thumbs down!