Possible Clues:

• Blocked at The Crucible?
• Put in situation hard to get out of? Possibly, providing one red's OK
• Derek (like the Naked Rambler?)'s repelled and thwarted
• Blocked at the table
• Restricted at the table
• Restricted by O'Sullivan?
• Obstructed at the table
• Put in difficult position, needs rook exchanged
• Thwarted by awful crookedness not going to extremes
• Thwarted Derek turning up, having cropped scarf on top