Trapped pieces are the extreme examples of poor mobility. They are awkwardly placed and often endangered. A typical example of a trapped piece is a white Bishop on h7 blocked by the black pawns on f7 and g6. Most of the time it gets eventually captured, but it takes so much time that can be easily pushed over the horizon. Most of the time the best thing such a bishop can do is to sacrifice itself for a (second) pawn, so its value should be decreased by about 150.
- a white knight on h8 in presence of a black pawn either on h7 or on f7
- a white bishop on h6 with black pawns on g5 and f6 (this one should be scored less severely, perhaps -50)
- a white knight on h7 with black pawns on g7 and h6
- a white knight on h7 with black pawns on g7 and f6
- a white rook on h1/g1/h2/g2 with a white king on f1 or g1 (perhaps -40, to prevent pseudo-castling with a rook hemmed in)