Plants vs Zombies Garden Warfare keeps crashing when I'm in-game.

Things to check..

1. Update your graphics driver.
2. Update your sound driver.
3. Update DirectX.

So if you're playing a game, and it's slowing down or crashing, take a look at what other programs you were running at the same time.  Your anti-virus program should always be running in the background, sure, but if it's downloading updates or running a scan of your computer, then that's going to cause a resource drain that could affect your game.