In sport combat such as boxing, kickboxing, mma (ufc, etc), one trains with rules, drills of specific combinations, is equipped with safety gear (hand wraps, gloves, head guard, etc), fights in a controlled environment such as a ring, cage, mat, etc, has set time limits, is overseen by a referee, and is governed by strict rules of engagement. The focus is on finishing the fight within the defined rules and in an acceptable manner set by the sanctioned event.
Whereas reality based martial arts such as Krav Maga, Wing Chun, Bak Mei, etc focuses on pragmatic self defence methods, multiple opponent engagements, targeting of “illegal” areas such as the groin, eyes, spine, etc, trains striking without the use of padded gloves, and defence against armed opponent(s), which in turn is more suited for the reality of the street as there are no refs, time outs, and perhaps there is more than one opponent. The main goal in self defence is to do what is necessary in order to protect oneself or loved ones and to ensure survival.
While combative martial art in either form promotes effective striking, the difference stems from the mindset, and the specific targeting of striking areas of the body. In sport combat, you are looking to execute strategies and a plan that was practiced in advance, to gain the upper hand on your opponent. With self-defence, you are training so that, should the need arise, you can react/respond effectively, appropriately and swiftly, working on trained instinct and reflex to do all that is necessary in order to survive.
In the end after all a punch is just a punch and a kick is still a kick, it is how one trains in purpose, mindset and striking intent.