Ganging up (multiple players attacking one): ejection from match; Strikes from behind, head-kicks, hitting downed opponents: ejection from match; Unsportsmanlike conduct / fighting outside ball-play: ejection
Why people argue about this
People often assume that the immediate ejection for ganging up is just about physical contact, forgetting that it also covers unsportsmanlike tactics like taunting or deliberately interfering with an opponent's ability to play. The confusion arises because they overlook how this rule extends beyond direct physical aggression to include any behavior deemed unfair by the referees.