Really can't see what the problem with Kurtz is. Agree with previous posters, he had a bad crash at BV last weekend and probably aggravated a previous injury. I don't ride a motorcycle myself but if that crash happened to me, I probably wouldn't want to ride ever again!
Anyway, BV are more or less guaranteed a play off place so why risk racing tonight when he has a GP at the weekend. He's riding for personal glory ( the ultimate dream as a speedway rider ) so if he had a bad come off tonight he'd be asking himself, why the hell did I ride tonight when there was not alot riding on it. Sensible decision in my view.