From Jorge Figueredo’s Cuban Baseball: A Statistical History, 1878-1961, p. 7 (on the 1879/80 Cuban League season):

Pitcher George McCullar and catcher Urban Carpenter became the first Americans to play (for Colón) in the Cuban league.  Oddly enough, the other teams objected to their presence when McCullar struck out 21 Habana batters in a game and also belted the first home run.  When the circuit high command upheld the protest, Colón withdrew from the competition and the Americans went home.

And from Roberto González Echevarría’s The Pride of Havana, p. 100:

In the 1879-80 season Colón Base Ball Club hired two Americans—Carpenter and McCuller, a pitcher and a catcher—who so dominated the games that other teams refused to take the field against them.

I’ve always been curious about the identity of these U.S. players who so outclassed the Cubans.  Neither Urban Carpenter nor George McCullar played in the major leagues, and I couldn’t match them with any minor leaguers at the time, either.

However, I was able to find passport applications for two men who had played for the National League’s Syracuse club in 1879, James F. Macullar (who managed the club briefly) and Warren W. “Hick” Carpenter.  The applications are dated September 24 and 25, 1879:

Neither application mentions their destination.  But according to Figueredo, the Cuban League season started on November 11.  Colón played only two games, one against Habana and one against Almendares, winning both; the club withdrew from the league on January 11, 1880.  And on the passenger manifest for the steamship City of Veracruz, arriving in New York from Havana on 15 January 1880, we find “James F. Maculler” [sic] and “W. W. Carpenter” (at the bottom, partly obscured by a crease), both 24 years old:

(click to enlarge)

Obviously, as the dominance of these players (or Esteban Bellán, for that matter) shows, Cuban baseball was just getting started.  (By some curious coincidence, both Carpenter and Macullar were left-handed infielders in the majors.)  Perhaps a more interesting question is what official reason was given for barring them from the league.  Was it because they were foreigners?  Or was it because they were paid?

UPDATE 12/21/2007  Adrian Burgos correctly identifies Macullar and Carpenter in his book, Playing America’s Game: Baseball, Latinos, and the Color Line, p. 32.  My only quibble is that he refers to them as “future major leaguers” (they had both already played in the National League).