Active rooks

A rook sitting on its own back rank, walled in by pawns and pieces, does very little. This module covers two well-known, unrelated ways a rook becomes genuinely active -- the detector reports both under the same label, but they're worth understanding separately.

The first is a rook that has infiltrated the opponent's 2nd rank (or, from black's side, the 7th rank) -- the rank where the opponent's pawns started the game and where many of them still sit. A rook there attacks pawns sideways, along a rank they usually can't be defended from, and can also help cut the enemy king off entirely from crossing that rank. Two rooks doubled on the 7th (sometimes nicknamed 'pigs on the seventh') can be devastating even without any other pieces helping.

The second is completely different: Tarrasch's rule, which says a rook belongs behind its own passed pawn, not in front of it. A rook behind the pawn pushes the pawn forward while staying safely out of its way and ready to support a promotion; a rook stuck in front of its own pawn actually blocks the pawn's advance and can even get trapped by it in some cases. This applies specifically to your own passed pawn, not just any pawn.

Both situations get flagged as the same 'rook activity' motif because they share the underlying idea -- a rook doing real work instead of sitting idle -- even though the geometry (rank vs. file, attacking vs. supporting) is different.