From TF2 Wiki
The Jag is an unlockable community-made melee weapon for the Engineer. The Jag was released on the 18th of December as part of Team Fortress' Áustralian Christmas' update. It was first found fully textured in the Team Fortress 2 game files after the Mann-Conomy Update, and was displayed in the Steam Update image for the Mann-Conomy Update
At the moment, the Jag's effect is barely noticeable, decreasing the time required to build sentries by less than a second. It is, however, slightly more observable in the building of dispensers, though the difference is also fairly minuscule.
- Due to the hook, the Jag's upper half strongly resembles the mathematical symbol Pi.
- According to Robin Walker in an email to community author Jman, the Jag was originally intended to be a part of The Engineer Update, and was eventually cut when Valve couldn't figure out attributes for it. The Jag was later added to the game as part of the Australian Christmas update.
- The name "jag" may refer to a particular manufacturer of cars which many people affectionately call jags.
- The Jag now has a unique kill icon.
The Jag appears to be what is the PDQ out of beta.