you soft seized. No biggie, but you should have really stopped the bike, let it cool, and then ride it home slowly. Something is obviously wrong with the engine (i.e. it's jetted too lean, you have a too hot plug, the air filter is off, etc) so you should figure out before riding again. You should check the piston and cylinder though. You will probably have these four polished stripes in the side of the piston. Also, check the under side of the piston. Is this brown, black, flaking, etc.? Also, what do the polished marks on the piston look like. A common soft seize will cause the four striped lines, which mean there is a problem with your rings, piston, the profiling on your head, or carb. problems (The good kind of soft seize). Other, single stripe marks mean worse problems. If you line up the marks with their prospective port, you will be able to find where the problem is. For example, if it lines up with the exhaust port, something is wrong with the exhaust gasket, or your pipe. I'm sure you got the idea. Best place to look for info on reading a seize is in moto-cross articles. I don't want to type it all right now but it's important to read a seize correctly to solve the real problem form happening. If after the bike cools you have a large loss of power, you can replace the rings and hone the cylinder (auto shops carry hones that attach to electric drills). You should do through two sets of rings per piston but it's not worth boring out the cylinder on a soft seize. Hope it helps. Bye.