While listening to Steve Stone on WSCR, 670 AM in Chicago on Monday morning, he made the following statement (which can be found here beginning at the 3:16 mark on the podcast):
"You very rarely, if ever, win a division under .500 at home. I can't remember a team that did that."
Easily enough checked, and guess what--as he is on most baseball-related matters, Steve Stone is correct. This first chart shows the winning percent of all teams from 1901-2011 during the regular season:
The average winning percent is .542, or the equivalent of a 88-74, which will put teams in the running for the wild card in almost every year. It would be fun to measure, and I have the data for the NFL (but not the NBA), but I suspect that baseball has the smallest home-team advantage of the three, but that's a post for another day. This next chart shows the home winning percent for the playoff teams during the regular season:
If it isn't obvious, the playoff teams have spectacular winning records at home during the regular season--the average is diminishing over time (as parity between the teams increases), but it's still .655, or the equivalent of a 106-56 record, a record that has a pretty good chance of getting a team in the playoffs.
To take it to the next step and test Stone's statement, he is essentially correct. There is ONE team that made the playoffs with a losing record at home--the 1981 Royals. However, the 1981 year was a strike year that introduced divisional playoffs between the winners of the two halves of the season, and as such it wasn't a traditional playoff format. Other than that, NO TEAM has ever made the playoffs with a losing record at home during the regular season.
Let me state this another way. Since 1903, of the 370 teams that have made the playoffs since 1903, ONE didn't have a winning record at home--and 369 did. As is typically the case, Steve Stone was correct and adds another marker to look at to see how good a team's chances of making the playoffs are. For all you young broadcasters out there, the career of Steve Stone would be an excellent one to emulate.