If you carry a .25 caliber be sure to aim at the teeth, any place else and you'll only piss the guy off. I'm 6'4" tall, 270# and most undesireables would rather pluck a hair off King Kong's butt than mess with me. I carry a Big Brute scoop that has a sharpened edge for water hunting. Retreat into knee deep water where running is impossible and start swinging.

Land Sharks, I carry a SCUBA knife like Sandman has on my tool holder, with a Gator Digger that's sharpened and two probes: on 12 inch brass and the other is a 18 inch Ice Pick probe. Ask a thug sometime how they like ice picks, most don't for good reason, it'll go right through a breast bone like a hot knife on butter.
Pepper spray is expensive but a
better choice is WASP SPRAY. It'll shoot a 30 foot stream and offer several shots for a few bucks. Also it's poison and the thugs will have to seek medical treatment to get the stuff out of their eyes and bloodstream.
If you are grabbed from behind, drive your heel onto their foot and use your elbows to their face. Don't bother with a groin kick, back slap them across the Adam's apple with the back of your hand.

That paralyzes their ability to breath and makes their eyes water. Other tips, go to Youtube and watch some of the Self Defense videos

that instructors put on there.
You might have to fight for your life so toss away the rule book and fight like a Barbarian

and fight to win. Most thugs are bullies and cowards and don't want to mess with someone who might kick their butt. Be safe!