How do you defend when the opposition goalkeeper joins as an extra player?

You have two sensible options, and the team should recognise which picture is available. One option is to allow the goalkeeper to have the ball while the two strikers screen passes into the centre-backs or midfield. The keeper is free, but the next pass is controlled. The second is to send one striker when the goalkeeper takes a poor touch or moves into a predictable area. The nearest midfielder must then step towards the spare player. What will not work is one striker chasing the goalkeeper alone while every passing option remains open. Use a game where the goalkeeper joins outside the box and reward the defending team for forcing play backwards or towards one side. At U13, the extra player is a numbers problem. The press needs a shared decision, not more running from the first forward. Let one striker approach the goalkeeper while curving the run to block one centre-back. The second striker screens the other central option. The nearest midfielder prepares to jump if the goalkeeper finds the spare player. If the distances are too large, hold the front two in screening positions rather than chasing.