My buddy Dave had the same thing happen at a race in Ohio last year. He had this cheap plastic hood on his 70-200 and it popped right off when he bumped the tripod. Of course it rolled under the bleachers and he never found it. He ended up cupping his hand over the end of the lens like a visor for the rest of the day. Looked like a total fool but his shots came out fine. Sometimes the free fix works better than the $18 one.