A clean sheet bet is placed on a specific team to not concede any goals during a match. If the team keeps a clean sheet (the opponent fails to score), the bet wins. If the opponent scores even once, the bet loses. The market is available for both the home and away team independently.
Clean sheet probability is directly related to defensive quality. Teams with solid goalkeepers, organised defences, and a low goals-conceded average per game are more likely to keep clean sheets. Top clubs in major leagues might keep a clean sheet in 35-45% of matches. Weaker defensive sides might average only 15-20%.
Relationship to BTTS: the clean sheet and BTTS markets are inversely related. If Team A keeps a clean sheet, BTTS is automatically No. If BTTS is Yes, neither team kept a clean sheet. Many bettors use one market to inform the other — if you think a team's defence is particularly strong on a given day, clean sheet Yes and BTTS No are both relevant selections.
Home vs away makes a significant difference. Most teams have notably better defensive records at home — partly due to the crowd advantage and partly because home teams tend to dominate possession and territory. An away team keeping a clean sheet is harder and generally carries better odds.
Example
Liverpool host a lower-league side in a cup match. Liverpool's clean sheet odds are 1.50 (66.7% implied). Over their last 10 home games against similar opposition, they have kept 7 clean sheets (70% rate). The 1.50 price aligns with historical performance. A £30 bet returns £45 if Liverpool keep a clean sheet.