The “Uncaught Third Strike” Mechanic is used by the Plate Umpire when the batter becomes a runner due to the third strike not being caught with first base unoccupied or two outs.
There are four possibilities that can occur with an “Uncaught Third Strike”: Obvious, No Catch, No Tag, and Tag.
This video will cover the Tag possibility. If you have not watched the “Out” mechanic video, you may want to do so prior to watching this video.