Graze from sabre unsheathed when principal spins around (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

ABR ( letters remaining in S ABR E when the outer letters S and E are removed [unsheathed]) + AS (when) + ( NO [number] + I [Roman numeral for one] – number one [principal]) reversed (spins around)