After a tough home loss to the Ravens, the Steelers traveled to San Diego to take on the Chargers.  The Chargers scored first in the first quarter when Philip Rivers found Antonio Gates on a 12-yard pass for a 7-0 lead.  The Steelers got on the board in the 2nd quarter when Chris Boswell nailed a 47-yard field goal for a 7-3 game at halftime.  After the break, the Steelers took the lead as Antwon Blake picked off Philip Rivers and returned it 70 yards for a TD and a 10-7 lead for the only score of the period.  In the 4th quarter the Chargers scored 10 points first tying the game 10-10 when Josh Lambo kicked a 40-yard field goal followed up by Rivers and Gates hooking up again this time on an 11-yard TD pass for a 17-10 lead.  The Steelers tied the game back up when Michael Vick found Markus Wheaton on a 72-yard TD pass for a 17-17 game.  The Chargers retook the lead when Lambo kicked a 54-yard field goal for a 20-17 lead.  Getting the ball back with less than 2 minutes left, the Steelers drove down the field.  Le'Veon Bell ran for a TD from a yard out to win the game.  With the game 23-20, officials had to review it to make sure he reached in before his knee hit the ground.  The call stood and then Boswell kicked the PAT for a 24-20 victory. The Steelers defense continued their surprising resurgence of sacks and takeaways by sacking Rivers twice and getting two more turnovers. The offense scored on their final possession as time expired to clinch a much-needed road win against the Chargers. The win improved the Steelers to 3-2 on the season and snapped a five-game losing streak in California.
Question: How many points were the Steelers trailing at halftime?
Answer: 4