Unlike sports where the goal is to get huge such as football, rugby, and weightlifting, combat sports such as boxing and MMA involve strict weight limits and technique prevails over raw musculature. For these combat sports, cardio, conditioning, and raw speed is much better than slow bulky strength. These aspects do not usually translate to musculature, so it can be difficult to tell who is actually trained in such sports and who isn’t.
It is because of this that it becomes very difficult to spot who is trained in martial arts and who is not. Most people have no training in martial arts, but you can always make the huge mistake of starting an altercation with someone experienced. You can be lucky and they will teach you a lesson without harming you too badly, or you may not be so lucky.