Billy Wagner came in for the bottom of the ninth tonight to preserve a one-run lead for the Mets, and proceeded to allow the bases to fill with no outs -- and then allowed no runs (a 5-2 ground ball out at home, followed by a 4-6-3 DP), preserving the Mets victory.
The average number of runs that score in an inning of a major league baseball game after bases loaded and none out occurs is about 2.4 runs. (source, Tom Ruane's run expectancy research at retrosheet.org and confirmed here: http://www.insidethebook.com/ee/index.php/..._run_frequency/).
Acording to the run expectancy finder at walkoffbalk.com, from 1977 to 2006 there were 68 games in which a home team with a one run lead in the 9th inning faced bases loaded and none out. The home team won 26 of those games, a winning pct. of .382.
Back at "The Book" blog (see link above), we can see that a team is held scoreless in an inning, after it gets the bases loaded and none out, only 12.2% of the time.