"Palladium \Pal*la"di*um\, n. [L., fr. Gr. ?, fr. ?, ?, Pallas.]
1. (Gr. Antiq.) Any statue of the goddess Pallas; esp., the
famous statue on the preservation of which depended the
safety of ancient Troy.

2. Hence: That which affords effectual protection or
security; a sateguard; as, the trial by jury is the
palladium of our civil rights. --Blackstone.

In definition 2, "palladium" = security so the phrase meant "in the security of the club".