Heavy rush

From TF2 Wiki

The Heavy rush is a tactic where you use the superior health and firepower of multiple heavies to create a steamrolling vanguard few teams can withstand. However, with low mobility and the absence of medic partners this can prove a risky tactic. Eventually, the enemy is likely to overpower you and your slow speed may prevent you reforming the vanguard before the enemy have set up stronger defences. On an unprepared foe this tactic can be devastating, though they are likely to be prepared a second time.