Police responded to a man who was threatening to harm himself with a knife. He stabbed himself and threw parts of his own body at the police. The officers withdrew and called for the SWAT team. They tried to use OC spray on the subject but with no effect. This may have been a good opportunity to use a Taser, but they may not have had one, or there may have been a reason it would have been impractical.
There are several dangers with this type of call. A man with a knife can cover a lot of ground in only seconds and can turn from threatening himself to threatening others very fast. He may also try and become a suicide by cop victim. There is also the problem of HIV or other disease or drug exposure to the police.
In my opinion, backing off was the right call. Clearly the subject was on drugs or mentally ill or both. A SWAT team has training and equipment that street cops don't have. They really needed a prison extraction team, the type that pull recalcitrant inmates out of their cells. Using special shields and puncture and liquid resistant clothing they can close grapple with prisoners armed with edged weapons and are unlikely to be injured. I have even known of instances of officers using a fire hose or a ladder to pin a knife armed suspect against the wall or the ground and disarm them. The key here is use your imagination and don't get yourself killed trying to save someone from trying to kill themselves; that's what the SGT Says.