Nappa powers up and then charges at the opponent to deliver a powerful punch to their arm, capable of severing it, causing excruciating pain and major damage to the opponent.
Nappa uses this attack during his battle against Tien Shinhan. After powering up to combat the Z Fighters, Nappa chooses to fight Tien first and attacks him, scorching Tien's arm in the process. Nappa then attacks Tien with the Arm Break rush, severing Tien's arm and mortally wounding him.
Video Game Appearances
Arm Break was named in the Raging Blast series and Dragon Ball Z: Ultimate Tenkaichi, where it appears as one of Nappa's Super Attacks. In those video games, the move does not sever the victim's arm, but it is clear that they are in great pain.
In Dragon Ball Xenoverse, it appears as a super skill under the name Arm Crash (アームクラッシュ, Āmu Kurasshu) and is chargeable. When fully charged it is capable of breaking an opponents guard (a reference to the fact that Tien lost his arm despite bracing himself due to the power of the attack). It is one of Nappa's Super Skills and can be obtained by the Future Warrior in Parallel Quest 05: "Attack of the Saiyans".
"Holding the button extends the distance traveled and increases power, which is good for attacking far-off foes. This technique can break an opponent's guard."
In Dragon Ball Xenoverse 2, it returns under the name Arm Crash and is one of Nappa's Super Skills. It can be learned by the Future Warrior by completing School Quest: Lesson 1 of Nappa's Training. Like in Xenoverse, it is capable of breaking an opponents guard. In addition to the Future Warrior it also appears as part of Turles' skillset when he is fought in the main story and in Expert Mission 05: "The Galactic Tyrant". After the 1.09.00 Update, it can be added to Bardock's custom skillset after it has been purchased for 5 TP Medals in Partner Customization. It can also be added to Turles' custom skillset for 5 TP Medals as well, while Nappa has it available by default. As it is used by low class soldiers like Turles and Bardock, in addition to mid-class soldiers like Nappa, presumably it was a common technique among members of the Saiyan Army.