We talking about BB's that can be stopped by a heavy jacket (ahhhh, childhood memories), or are you thinking about the pellets from those 1,400fps monsters that people use on small varmints? Initial thought is to get myself where I can't get shot anymore, call 911 and be prepared to use force if the attacker pursues.
Ultimately, yeah, it's a BB gun. But some of those can put out some speed and can cause some real damage. Not typically fatal, but a lucky shot could do some permanent injury. You're already being shot at, so you've got little tactical advantage standing your ground if you think returning fire is even prudent. Call PD, let them handle it, press charges to fullest extent of law.
I remember growing up walking along the bank of the Santa Ana river and getting shot just abover the knee by some little effer on the other side of the river. I can't remember what I did/yelled at him, but I didn't get shot a second time. lol. He was probably trying to hit me in the balls and didn't plan for BB drop. Haha
Pellet guns range from Nerf gun power to big game hunting.
I have a Benjamin airgun that fires a .357" 105 grain pellet at 800 feet per second. Being hit by it is really is no different than being shot with a .380 ACP from a handgun.
Evanix makes a .22 airgun that is as powerful as a .22 short. I've heard some ranchers put down cattle with a .22 short.
I have .177 air rifle I bought at Walmart for less than $75. It can fire BBs and .177 pellets. When it was new it could shoot through 10 tin cans lined up with a steel BB.
I wouldn't shoot someone if they were firing 6mm plastic pellets at me, but if they had something that flings metal down range then they may be a lethal threat. A BB or small lead pellet could kill you, and even if it does not it is highly likely to cause serious injury.