Freestyle · Pattern
Open four.
Four connected stones with both ends open give you two immediate winning points. If your opponent can answer only one and has no immediate win of their own, the other end wins next.
F9–I9: both ends (E9 and J9) are empty.
Try it: make an open four
This page covers contiguous straight fours. It does not cover VCF, Renju forbidden moves, or the full family of broken/jump patterns.