Often there is that moment in a boxing match where a fighter strikes a solid punch that rattles their opponent for a split second. A skilled fighter will seize that advantage and press it for the knockout. This rule holds for most sports – one player gains an advantage (either through their own skill, their opponent’s mistake or both) then if they see that advantage and can press it, they score and/or win.
Taking the angle in martial arts is a major advantage. People’s power, vision and coordination lie largely on the front side of their body. Get to their side or back and they are weak, can’t see you and can’t summon up all their limbs to resist your strikes.
Lesson: get the angle and either keep it or getting an even better angle by softening up your partner (striking).