Hello

For some reason my red cat shockwave axle keep popping out. Nothing seems to be broken or damaged. I put it back in drive it a little while thing pops back out so I know nothing is broken. Any ideas or suggestions to fix it. This is my first car is awhile

front or rear?
Either way, I always used either some small O rings (from hardware store) or short pieces of nitro fuel tubing to keep the driveshafts in place. The driveshafts have to be a bit short in order to allow compression of the suspension...but this also allows them to move far enough out of a drive cup to pop out (usually especially on the front, where steering+suspension flex create more movement)
Thus, I put the O ring or bit of fuel tubing into each drive cup. This helps "center" the driveshaft and still allows it to move some with the suspension. After you put the O rings or fuel tubing in, move the suspension (compress) and make sure the driveshaft isn't too tight or doesn't bind up. If it does, you need a thinner O ring or a thinner piece of fuel tubing.
I did this on my volcano and tornado's.