If your holder (or rider, who knows? in this instance) doesn't know what the hell is up it's possible to fly off like that, or break a chain.

I had a holder once, instead of holding the seatpost fingers open so the bike would slide out on acceleration he had it in a deathgrip fist closed, gun goes, legs activate, faster than he released and BanG, broken chain FTL. In a CMWC final no less. I cant see my seatpost looking up a hill ready to sprint, but I know my trackstand is good enough that I didn't think he was gripping, just supporting, but no, deathgrip was activated.

I hadn't even wanted a holder but everyone else had one. I did well in the heats so it wasn't a complete loss, except teh part where I lost completely in the final.

Did a terrible wheelie (no holder, all me) on the start of a heat, made my legs fly off all crazy and had to get it together and sort of restart after, everyone else had long pulled away buy 3-4 seconds. It worked out though because the sprint was uphill and the other riders hadn't known/prepared with proper gearing? or were ust slow, but uphill was a surprise for some. Anyway I got my bike back beneath me, clipped in and went thinking it was all over, but the all 3 guys in front of me seemed slo-mo stretched in a line, so I slalomed them as I went up the hill and won.

Oh to be fast again, and yeah, I was on a road bike facing fixies on an uphill sprint.