For more examples, click here. Disclaimer: there are fewer of these floating around than we would've assumed, which suggests some video tagging tomfoolery of some sort.

An Error on a Pickoff Attempt

A runner takes a lead off from their base. Maybe they're already planning on stealing— maybe they've even actually started running on a previous pitch that was fouled off. Maybe they just have a good reputation as a base-stealer, and the pitcher is being vigilant. Or, maybe the runner is just minding their business, and the defense puts a pickoff play on.

No matter what the circumanstance, instead of making a pitch, the pitcher throws to the base in question, hopefully managing not to balk along the way. Unfortunately, things go a little sideways on the throw— maybe the ball bounces in the dirt, and the fielder can't corral it. Or, maybe the throw absolutely sails on the picher, escaping into the outfield, or into foul territory. No matter the circumstance, now the defense has a problem; anyone on base is now free to run to their heart's content¹, until the defense can get control of the ball, at which point they can potentially try to throw a base runner out. Again.