Q: How often does this happen - a pitcher walks four batters in an inning without allowing a run?
A: Only seven times in the last ten seasons.
"On Friday night, Pirates rookie Juan Perez was thrown out there to start the ninth inning in a game the Pirates were losing, 8-2, and proceeded to walk four of the first five batters he faced.
Fortunately for him, the middle batter in that sequence was a leading contender for the highly-coveted title, “Slowest Man in the Major Leagues.” (Also known as “Slowest Member of the Molina Family.”) Bengie hit into a double play; Russ Ortiz would thus come to the plate with the bases loaded and two out, and when he flied out Perez had escaped the inning without allowing a run to score."
List of "achievers" linked below.
http://www.baseballprospectus.com/unfiltered/?p=330