Question: What is the penalty if I discard the winning tile to another player?

Answer: If you are not playing for points or money, there is no penalty for throwing the winning tile. However, becoming a strong and defensive player means knowing when not to throw an obvious winning tile to a player and when to break up your hand. Quoted from the National Mah Jongg League in the 2020 Mah Jong Made Easy publication, “remember, it is just as important to prevent the other players from completing their hands.”  “YOU CANNOT MAH JONGG SECOND.” 

If you are playing for points or money, the  person who discard the tile pays the winner double the value and all others pay the value as shown on the card. 

Source:  Mah Jongg Made Easy (2020 page 18, Defensive Playing;  page 26, Standard Scoring)