I have the ball. My back is to the opponent's goal. My teammate, further from but facing the goal, is running toward me and toward the goal.
Rather than turn and shoot, I pass the ball back to my teammate who immediately shoots.
Am I offside?
Obviously, at the moment your teammate touches the ball, you are in an offside position (supposing all defenders are further from the goal, otherwise you wouldn’t be asking, I guess). But being in an offside position is not an offence in itself.
To be penalised for offside, you’d need to be
[…] involved in active play by:
- interfering with play or
- interfering with an opponent or
- gaining an advantage by being in that position
(FIFA: Laws of the Game 2015/2016, Law 11 – Offside)
The official Interpretation of the Laws of the Game and Guidelines for Referees defines those terms in this way:
- “interfering with play” means playing or touching the ball passed or touched by a team-mate
- “interfering with an opponent” means preventing an opponent from playing or being able to play the ball by clearly obstructing the opponent’s line of vision or challenging an opponent for the ball
- “gaining an advantage by being in that position” means playing a ball:
- i. that rebounds or is deflected to him off the goalpost, crossbar or an opponent having been in an offside position OR
- ii. that rebounds, is deflected or is played to him from a deliberate save by an opponent having been in an offside position
- A player in an offside position receiving the ball from an opponent, who deliberately plays the ball (except from a deliberate save), is not considered to have gained an advantage.
In your situation, it means you would be offside if either
Otherwise, the pass-back-and-shoot is completely legal.