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, as when you beat someone really badly at tennis, you could say "you throttled her," but nobody has to get hurt.