We can find the answer by turning to Major League Baseball. Unlike the NFL, which televises every game nationally, MLB games are usually only broadcasted through local television stations. Every club has their own TV announcers travel with the team to call games, and unfortunately, many of them seem to be packing their pom-poms and fan jerseys in an effort to root on the home team.
A recent WSJ study confirms the bias. After watching game broadcasts of all 30 teams, they proceeded to rank the commentators in an "announcer bias index." Of the 30 teams, 25 broadcasts included at least one remark favoring the home team, while the Blue Jays, Yankees, Red Sox, Mets and Dodgers remained objective.
But the bias goes even deeper. Take for example Ken "the Hawk" Harrelson, play-by-play television commentator for the Chicago White Sox. Infamous for his unbridled homerism, fanatic home run calls, and lack of excitement at opposing teams' success, Harrelson's broadcast had an astounding 104 biased comments--by far the most of any team. Here are two of the Hawk's actual home run calls, the first a Conor Gillaspie shot in the seventh inning to take the lead against the Rangers:
...and this one, a Nick Swisher blast that put the Indians up a run against the White Sox:
"And the payoff…it is a nine-eight…Indian lead…four runs here in the top of the ninth inning..."
Although objectivity is dying out in baseball, there is still a flicker of hope. Vin Sculley, the voice of the Dodgers since the team was stationed in Brooklyn, remains one of the greatest broadcasters of all time. He never refers to the Dodgers as "we," "us," or "our," doesn't create pet names for players, never gets too high or too low. He has the calling of critical plays down to an art form; showing appropriate excitement without getting carried away in the moment. (Notice that after calling Kirk Gibson's home run, he remains silent for an entire minute and seven seconds, letting the listener soak in the reaction of the crowd. Not many can do it the way Vin does it).
Baseball doesn't need TV announcers screaming at fans whenever a home run is hit for "their" team. Any glorified fan with a microphone can do that. The magic of the game deserves a higher plane of analysis and commentating.
Like the magic that emulates as Vin Sculley calls a game.