Possible Clues:

• Football blunder
• Self-inflicted damage that hurt along with treatment
• Action which backfires on one
• No-go law (anag.)
• Confess on purpose action proving personally disadvantageous
• On the pitch that hurts a long way
• Knock the ball into the wrong net to score it
• Error made initially by Google's central characters
• Footballer's error
• Breaking law, go on conceding this is a mistake