What kind of car? Some cannot run in the grass, because you can overheat the clutch and the clutch shoes will melt into the clutch bell.

Tell us: car, engine, etc.

The clutch is inside the round cup/bell shaped thing with the gear on it that comes out from the engine shaft. The clutch allows the engine to run without the wheels moving. Once revving strong, the clutch kicks out and catches the clutch bell, and power run thru the tranny/gears/shafts and moves the car.

When there is alot of drag from grass, or you have an obstacle you force/power through it, some weaker clutches melt and bind the bell. Bigger vehicles with heavy clutches and ample power/grip/clearance can run in grass w/out melting the clutch, but even they can have melted or shortened clutches if abused.