The 1991 Washington Redskins season started with a franchise-record 11 straight victories. Also during the season, "The Hogs (American football)", under the coaching of Redskins offensive line coach Joe Bugel, allowed a league low and franchise record nine sacks – the third lowest total in NFL history. The 1991 Redskins offense also dominated under the brilliant coaching of offensive minded head football coach Joe Gibbs scoring 485 points which was the most by any team in the 1991 NFL season. The 1991 Redskins defense was also dominant under the coaching of defensive coordinator and guru Richie Petitbon, giving up only 224 total points which was second best of any team in the NFL in 1991, while also not allowing a single point to opponents in 3 of the 16 games played that season. After posting a 14–2 record, the Redskins made and dominated the 1991–92 NFL playoffs, beating the 1991 Atlanta Falcons season and 1991 Detroit Lions season by a combined score of 64–17.  On January 26, 1992, the Redskins won Super Bowl XXVI by defeating the Buffalo Bills 37–24 with Mark Rypien winning the games Super Bowl MVP award. After the Super Bowl, the Redskins set another franchise record by sending eight players to the Pro Bowl. The 1991 Washington Redskins season are widely considered one of the best teams in NFL history.
Question: How many games did Richie Petitbon allow opponents to score points in during the 1991 NFL season?
Answer: 13