Lewis sent off Bradford midfielder Jon Worthington for a second bookable offence in stoppage time and also booked nine other players - four from the Bantams and five from Northampton.
Striker Jake Speight put Bradford in front from the spot after eight minutes when Cobblers right-back Seth Nana Ofori-Twumasi handled Kevin Ellison's cross.
But Shaun Harrad equalised for the visitors after 59 minutes after he had been brought down by defender Lewis Hunt.
He said: "We were disappointed we didn't win the game. We thought we did enough to win and were disappointed with the penalty that Bradford were given, but the lads kept going and kept their spirit. I thought our back four did well. They survived a bombardment. There were lots of free-kicks and corners and we had to deal with them.
"There were 43 fouls and 11 cautions in the match which is an extraordinary ratio. I don't think every foul that the referee awarded was a foul let alone a booking."
Source: PA
Source: PA