One-two combo

[1] In boxing parlance, fundamental punches are commonly assigned numbers by trainers and in this case there is the jab (#1) and the cross (#2).

[1] Boxers begin practicing the basics starting with offense and generally learn punches starting with the fundamentals - the jab (#1), the cross (#2), then onward to more complex punches such as the lead hook (#3), right uppercut (#4), and left uppercut (#5).

In this combo, the jab (lead hand) is designed as a range finder to close the distance between a fighter and their opponent to set up a power-punch (backhand).

[4] In a one-two combo the cross is the power punch due to the torque and rotation of the body required when using this technique.

[5] When this combination lands successfully, the boxer's jab is used to lift their opponent's head in order to expose their chin for their cross - resulting in the one-two combo.