Seen plenty, had to pull people out of some, had to get myself (thankfully not others as well, or at least those I was with were equally capable of doing what needed doing, or indeed jumping over fences) out of places in the past before it kicked off and on rare occasions have had to throw elbows, fists and do other less pleasant things to man (and woman) and beast. Sparring as well if that counts.
Aside from sparring it is not fun. Don't recommend it. Don't recommend getting involved with people that provoke such things (even unjustifiably). You might be in the right but a righteous elbow to the face of some moron still leaves you with a hurting elbow, possibly some legal questions* and you still run the risk that they are faster, better positioned, more determined (mental states and drugs don't mean much to your broken arm), armed and you missed it, with more friends than you realised (or thought would jump in) or just more lucky.
*people don't necessarily fall down and wake up with a bruise in the morning, or a little bandage. The human body is both surprisingly strong and surprisingly feeble, especially if you are conditioned to react as per the more dangerous martial arts (the marquis of queensbury does not exist in the real world -- eyes, genitals, joints that won't recover, internal bleeding, head injury... all real possibilities). This also says nothing about the rules around you -- I have been in places where if you start it then you are always in the wrong and you get what is coming to you, and I have been in places where a nice boot to the face (oh and I tend to wear steel toed boots everywhere) as they are lying on the floor so as to make sure I can run away will see me answering questions before the beak.
This is not to say I don't recommend being able to act** (in the heat of the moment it is a lot of muscle memory, and after the first few adrenaline dumps you learn to control it and maintain focus/awareness to a greater degree), being able to read situations (spot planned aggression, identify the leaders...), having situational awareness in general (not walking into blind corners and what have you) or similar such things. Still give the mugger your wallet or run like fuck if the situation is such where that is an option. Size and weight are not everything but they count for an awful lot, and while I as a fairly tall guy that is reasonably well built could probably be tossed around like a rag doll despite what training I have by some tiny oriental dude out there with years of training then that is very much the exception (said tiny oriental dude will probably also be the first person to extol the virtues of height and weight in such scenarios too).
**whether you want to be able to get completely aggressive and do what needs doing as far as being able to kill or intentionally seriously injure I can see avoiding as a plain old civilian.
