I have an older rear engine snapper riding mower. My son hit a soft ball and it turned off and wouldn’t restart. I replaced the flywheel key that was sheared but still won’t start. It has a spark but doesn’t seem to have compression. Any help is appreciated. Thank you

Check this out David. https://www.partstree.com/parts/snapper/mowers-rear-engine-riding-lawn-mower/381450hbve-84270-snapper-38-rear-engine-rider-14-hp-hydro-drive-series-0/38-deck-sub-assembly

get a flywheel puller http://www.bing.com/search?q=briggs+flywheel+puller&FORM=AWRE

model #under seat or hood?

unbolt the hub the remove the side plate on the side you need to change not as hard as it sounds like 7or 8 bolts

You may have damaged the flywheel key. This affects the timing of the engine, which results in among other things, hard starting and when running will not run as smooth. The flywheel key is the little metal piece that keeps the motor crankshaft engaged to the flywheel. It is designed to shear or partially shear to protect the engine from more sever damage from impacts.

I hope this helps, please let me know how it goes.

Do not run it like it is. At a minimum you have partially sheared the flywheel key. That upsets the ignition timing. Remove the flywheel and inspect the key, replace if any damage whatsoever. The key is a little piece of soft metal that is designed to give way when you hit something hard. After repairing that, remove plug and turn the engine over by hand to see if anything is hitting in the engine. Probably could do that first to let you know how bad it is. If no unusual noises from the engine or knocking of parts, try turning over with pull cord checking again. Then you can put the plug in and attempt to start it after flywheel key replacement.

I hope this helps.

make sure thers power going into the starter
if there is then see if the starter is siezed, try turning the fly gear, but not just up against the flywheel but try turning the starter backwards to see if it moves

He more than likely sheered the key in the crankshaft. When the key bends or breaks it throws the timing off and the engine will not start. The key is there to prevent damage to the crankshaft when you hit an object. You will need to remove the engine cover and then use a puller to remove the flywheel. Where the flywheel connects to the crankshaft you will see the key which is either broken or bent. All you do is buy a new one and replace it.

When you the key this time, put the flywheel on first then the key but this time use a little grit between the flywheel and crankshaft. Something like grinding compound. It will keep the flywheel from moving plus make sure you torque down the flywheel nut good.
HTH
Good Day.

Is it a push mower? Just curious...
Generally when this happens, the spark is firing out of time. What did this is probably a hard object was hit with the mower and the flywheel key was sheared or offset in shear. They are pretty soft and designed to take the brunt of such a hit to the engine.
Anyway, if this is the case, remove the flywheel and put in a new flywheel key.
Crank her up...