Sumo in Martial Arts Styles

[Kromm]

That kind of pushing isn't really handled well by Sumo, though. What you want there is covered by Teamwork, specifically:

Brace a teammate in front of him and within a yard, adding 1/5 (round down) of his ST or HP, as applicable, to his ally's score when his friend resists a slam (p. B371), executes a shove (p. B372), or suffers knockback (p. B378). This is a free action.

Note that with up to three people behind you, and the Shoves with Weapons rule on p. 112 of Martial Arts, you can get some pretty scary shield presses going. If Alexander, Bedros, and Cleon, all with ST 12, brace Drusus, also ST 12, then Drusus has effective ST 18. Behind a DB 2 Argive shield, he's doing a 1d+3 shove. That's 8-18 for knockback, averaging 13 . . . enough to knock a ST 15 man back and perhaps down. If Drusus' opposite isn't braced, he falls and is overrun.

These rules aren't really meant for mass combat per se, of course, but for individual combat. However, they get the point across.