Poteau
In short
A poteau is the vertical post that forms the side of a goal in football or rugby.
In plain words
It is the metal or wooden upright that stands at each end of the goal frame. The ball must go between these posts and under the crossbar to count as a goal.
A simple example
A striker kicks the ball with great force, but it hits the inside of the left poteau and bounces away from the net.
Why it matters
The position of the poteau defines the exact boundaries of the scoring area. If a post is moved or damaged, the rules of the match may be affected.
Easy to mix up
It is often confused with the crossbar, which is the horizontal piece at the top.