Something called 'Due Diligence' would probably cover the organisers.
If they can 'prove' that they have taken all reasonable precautions then they can't be held responsible for the actions of others operating outside of those precautions.
'Due Diligence' may simply extend to saying 'NO IPODS' on account of not hearing the marshalls instructions. If you don't hear the marshall shout "mind that lorry, stop!" and you get flattened, then they cannot be held responsible for your accident.
On the other hand, if for some reason the course sends you over Beachey Head, you may have a case. Or would have done.