It's really easy to get sucked in to racing a rival at a trackday. It doesn't take much to push just that little bit too hard. Maybe it's a show of a wheel, or perhaps just hearing a constant noise from behind, it's all you need to push hard. If you're behind and having a dice with another rider, then you're putting a lot of trust in that rider. He could be a cracking racer or an utter numpty on the edge. You just don't know, so it's good to be wary of getting sucked in.
If it all goes wrong with the rider in front, or even if they have a buttock-clenching moment, then it's bound to affect you – and if you're right up someone's chuff, then you could suddenly be sucked in to someone else crashing. But now's the time to keep your cool and to concentrate on where you want to be, rather than gawp at the misfortune of others. You still need to weight up a few things. If the rider has a front-end crash, then the chances are the motorcycle will naturally run to the edge of the track. All you need to do is to keep a tight line and you'll avoid the carnage. Highsides are a little different though as they tend stay a little closer to the racing line. A motorcycle flicking a rider a meter in the air is a pretty impressive, if unfortunate sight, but now's not the time to be a spectator. Again, tightening the corner is probably you best bet, although a rider could be dumped right in front of you.
Breathing is the key, again. Obviously, you don't want to running anyone over, but this could be the less of two evils. Running on the grass is another option, and is something that can feasibly be practiced; slowing through the gears, keeping steering input to an absolute minimum and avoiding big handfuls of front brake are crucial.