On average there are about 12520 nonfatal injuries per year (in which the prisoner attacked the guard)
About 11.3 fatalities per year (in which the prisoner attacked the guard)
Very few prisoners are injured or killed by guards- but the ones that are murdered get more publicity.
The prison guards evidently can't defend themselves as well as they need to.
Even though there are a few bad eggs, the vast majority of prison guards are not there to assault prisoners. Giving them non-lethal but very effective means of self-defense in a situation where they are surrounded by criminals who can and often do assault their guards is a no brainer.
This must be done.