This sound effect can be found on Foley Sound Library, which was made by The Hollywood Edge.
Sound Effect Description
Low End Punches; Heavy Punch With Low Thud And Light Bone Crack. - Fight Sweetener.
Clean, Full Length and Unedited Link to the Sound Effect
Used In
Abridged Anime
Image Gallery
It's Always Sunny in Konosuba! Hollywoodedge, Low End Punch Heavy FS040502
Audio Samples