The AA expanded to a previously-unheard of 12 teams in 1884. Actually, 13 teams played, but Richmond dropped out partway through the year and was replaced by Washington...part of the perils of a big expansion program. The added teams were Brooklyn, Indianapolis, Richmond/Washington, and Toledo. New York won the pennant, with Columbus, Louisville, St. Louis, Cincinnati, Baltimore, and Philadelphia making strong showings.
Dave Orr won the batting title with a .354 average, with John Reilly second at .339 and Pete Browning third at .336. Harry Stovey hit .326, Fred Lewis .323, Dude Esterbrook and Charley Jones .314. Stovey led the way with 124 runs (the games each team played had increased again, into triple digits now), trailed by Jones at 117 and Arlie Latham at 115. Sam Barkley had 39 doubles, Browning 33 and Orr 32. Stovey had 23 triples, Reilly 19 and Fred Mann 18. Reilly hit 11 homers and Stovey 10. Orr had 112 RBI.
Guy Hecker ran away with the league lead in wins with 52, next were Tim Keefe and Jack Lynch with 37. Tony Mullane had 36, Ed Morris and Will White 34, Bob Emslie 32, Bobby Mathews 30. Hecker also led with a 1.80 ERA, Morris and Dave Foutz 2.18, Keefe 2.25, Frank Mountain 2.45. Hecker completed his pitching Triple Crown with 385 strikeouts, Hardie Henderson was next with 346, Keefe 334, Mullane 325, Larry McKeon 308, and Morris 302.
AA Win Shares data; pitching; Guy Hecker (Louisville) 74, Tony Mullane (Toledo) 58, Tim Keefe (New York) 47, Ed Morris (Columbus) 44, Frank Mountain (Columbus) and Jack Lynch (New York) 36, Will White (Cincinnati) 33, Hardie Henderson (Baltimore) 32, Bob Emslie (Baltimore) and Bobby Mathews (Philadelphia) 31.
Position players; Charley Jones (Cincinnati) and Dave Orr (New York) 27, Dude Esterbrook (New York) 26, John Reilly (Cincinnati) 25, Pete Browning (Louisville), Candy Nelson (New York) and Arlie Latham (St. Louis) 23 each, Harry Stovey (Philadelphia) 22, Chief Roseman (New York), Tip O'Neill (St. Louis) and Sam Barkley (Toledo) 21.
WARP3 leaders, pitchers: Mullane 10.2 (best year), Hecker 10.0 (career year), Mountain 3.9 (only good season), Billy Taylor (Philadelphia) 3.3, Keefe 3.2, Morris 3.1 (as a rookie). Pitchers not among the leaders, but on the WS leaderboard: Lynch -1.2, White -2.5, Henderson 1.7, Emslie 1.8, Mathews -0.8.
WARP3 leaders, players; Jones 7.1, Esterbrook 6.3 (best season), Orr 5.8 (as a rookie, 53 AB the previous year), Reilly 5.2, Jocko Milligan (Philadelphia) 5.0, Barkley 4.9 (rookie, best year), Pop Snyder (Cincinnati) 4.7, Browning and Stovey 4.5, Latham and Fred Carroll (Columbus) 4.4. Players on the WS leaderboard but with lower WARP: Nelson 2.6, Roseman 3.2 (best year), O'Neill 0.1 (also a rookie, 76 previous AB).
WAR for pitchers: Hecker 16.6, Mullane 10.8, Morris 9.5, Keefe 9.4, White 7.7, Emslie 7.5, Lynch 7.2, Henderson 7.0. Position players: Orr 6.1, Esterbrook 5.2, Barkley 4.9, Reilly and Latham 4.6, Stovey 4.5, Sadie Houck 4.4, Jones 4.3.
Best pitcher: Guy Hecker. Busiest, and best. Led league in wins, ERA, strikeouts, innings, and WHIP. One of those "explosion" seasons, or career years.
#1 Guy Hecker, #2 Tony Mullane, #3 Tim Keefe, #4 Ed Morris, #5 Bob Emslie.
Best player: Dave Orr, leader in average, hits, RBI, and OPS+. This was his best year, but he would continue to be a star in the AA.
#1 Dave Orr, #2 Dude Esterbrook, #3 John Reilly, #4 Charley Jones, #5 Harry Stovey.
Best rookie: Ed Morris. Beats out Orr by a nose. Morris would pitch well for Pittsburgh for the rest of the decade.
Best manager: Jim Mutrie led New York to the pennant, and was one of the first non-playing managers.
Pass on the UA. I don't see the Union Association as a major league, and will disregard it.