Functionality

A Jail Arrow would surround a hit target with iron bars to trap it.

Proposed Recipe

One normal arrow surrounded by iron bars would yield one "Jail Arrow"

Proposed Effect Details

Hitting an entity would surround it with 8 iron bars, the same number used to craft the arrow. This is required to prevent the arrows from being used to farm iron bars.

Ideally the bars will completely trap the entity like in this image. However, because entities move, especially after getting hit by an arrow, it could prove difficult to pick the correct Locations in which the iron bars should be placed. (Maybe there's a way to prevent knockback, or to move the entity to a specific coordinate where it can be properly surrounded...)

An alternate approach would be to place the bars one block off the ground covering the perimeter of the 3x3 area immediately around the hit entity. This approach is more likely to successfully trap the entity since it covers more area, but it definitely doesn't look as neat.