Cooper's flag

the cat-tail (Typha latifolia), the long leaves of which are placed between the staves of barrels to make the latter water-tight.

See also: Flag

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
Linesman Anthony Cooper's flag stayed where it was and ref McLean waved play on to the fury of the home players and fans in the 4919 crowd.