I've been playing with building a Matrix, or categorical system to describe this phenomena and how it happens. It goes something like this; There are 4 types of combat. 1) The first being the "bully fight". This is what most people believe is da' streets, but really it's just a couple of egos huffing, puffing and posturing. Maybe punches are thrown. Most people grow out of this crap. 2) Sports fighting. This is fighting based on a specific rule set. Good fighters understand and utilize the rules to their advantage. 3) Sudden violence. This is the real da' streets. It's rare, and there are relatively few ways to prepare for it - but the military uses realistic scenarios. I think there are some martial artists coming close to this, for example the Spear System, or maybe Fit to Fight. But you can only do so much preparation. Key attributes would be good protective gear because in order to train this correctly, you'd have to make the scenarios as realistic as possible like blind-side a person, shove them into a wall and hit them with a baseball bat. See if any style can defend against that scenario
and the final 4) ritualized combat which is pretty much any traditional martial art. It's similar to sport based in that there are rules and etiquette.
A person can be really good in number 4) but be terrible at 2) and 3).
I think a key to success is understanding which category you are training in. So if you're training 4) and want to participate in something that falls in 2), then you should minimize 4) and train 2). If you're training 4) and want to include 3), then invest in high quality protective gear so you can really go at it and see what works in different scenarios.