Green’s Dictionary of Slang

1. (Aus./UK) a drunkard (who reels around).

1648		J. Taylor A brown dozen of drunkards 1: [heading] 1. Drunken Wimble-tree, ali-ass Reeler.
1895		C. Crowe Aus. Sl. Dict. 13: Butted a Reeler, met a drunken man.
1923		J.C. Goodwin ‘Criminal Sl.’ in Sidelights on Criminal Matters 164: Bill the fingersmith was a fair reeler when he had touched and had the skyrockets of his duds.

2. (prizefighting) a heavy blow that makes the recipient reel.

1842

Whip & Satirist of NY & Brooklyn (NY) 3 Sept. n.p.: Jim stopped him by giving him a reeler on his ‘dice box’.