The throttle of an engine controls the fuel going in, and if you're going at full throttle, you'd better hang onto your hat.
You can think of a throttle as a throat, and the two words may be related. But as with a throat, if you block a throttle, something bad is likely to happen. You can throttle your car — cut off the air to the engine, also known as applying the choke — and you might stall it out. You can also throttle a person — the image is that you grab the person by the throat and cut off his air. It's much better to use throttle figuratively: when you crushed your opponent at tennis, you could say "you throttled her" — but nobody really got hurt.