Last night in 3rd round my son's low 12 second camaro wouldn't go in 2nd gear it stayed in low . Coming back the return road said the car was shaking / vibrating and hard to keep moving , had to take drive shaft out to push it in the trailer. Has manual valve body. Any ideas what this could be ?

Sounds like he broke the intermediate sprag and maybe got some metal in the planetary and locked it up.

Drop the pan and see what you find. My guess would be what Trans Lady said.
The 6 million dollar question is how do you do a burnout? If it comes out in 2nd and grabs it will shock it badly and break the sprag and or the race.