I've had a fair few occasions where I drift far too left/right or spend more time airbourne than I really ought to at that area of the track, and end up clipping a trackside object or a bridge suspended above the track, causing me to be walloped away like a pinball, either right back across the track or into the air. I don't think the start/finish line could do something like that, so I guess, like me, you clipped an object that's right next to the trackside.