Those protesters had circled the police and were not allowing them to leave, going so far as to say "If you release your prisoners, we will allow you to leave".ApolloBoy wrote: getting pepper spray down their throats (which actually happened at UC Davis)? I think not.
That is a big no-no.
The protesters in question (those who are in that now-famous photograph) were informed by the very officer who pepper sprayed them, face-to-face, one-by-one, what the consequences of their failure to allow the police to pass would be, including an explanation of the affects of pepper spray on a person. He even went so far as to ask them if they understood and repeated parts of his explanation when needed.
These people were given over ten separate opportunities to move.
They chose to allow themselves to be sprayed, in part goaded on by the crowd who encouraged them not to move but did not take their place. The officer who sprayed them demonstrated a degree of professionalism and self-restraint that few people (myself included) are capable of.