The Padres selected Waldron's contract from Triple-A El Paso on Saturday ahead of his start against Washington.
The 26-year-old knuckleballer hasn't exactly been outstanding in Triple-A this season with a 7.02 ERA and 1.65 WHIP, but his unique arsenal of pitches could be enough to throw big-league hitters off their game a bit. Ray Kerr was optioned to El Paso in a corresponding move.