It can also be used like an action word " That QB just got slagged from behind."
2. To reduce something to slag i.e.
the vitreous mass left as a residue by the smelting of metallic ore.
from Low German slagge, from Middle Low German.
Slagged entered the realm of slang through its extensive use in Transformers: Beast Wars (1996) predating its use in Batman Beyond