After losing two straight games, the Raiders looked to rebound at Qualcomm Stadium, facing a Chargers team coming off a big win at Indianapolis. The game started well for the Raiders; thanks to a muffed punt by Darren Sproles that was recovered by Hiram Eugene at the San Diego 18&#160;yard line, and set up a 9-yard rushing touchdown by Jason Campbell. Scoring continued in the first quarter with a 4-yard pass from Campbell to Jacoby Ford; and gave the Raiders an early 14-0 lead over the Chargers.  The second quarter started with a 9-play, 48&#160;yard drive that ended on a 39-yard field goal by Nate Kaeding, giving San Diego its first points of the game. Oakland answered with a rushing touchdown by Michael Bush, extending the lead to 21-3. The first half closed on a missed field goal by Kaeding. The second half started with a quite calm third quarter, who saw both teams playing good defense and a Raiders team suffering with penalties. The third quarter closed with another field goal by Kaeding, nearing the Chargers on the scoreboard 21-6. The fourth quarter saw the Chargers trying to mount a comeback with a 4-yard TD pass from Philip Rivers to Antonio Gates; but it was promptly closed by a 7-play, 62&#160;yard drive that ended with a Darren McFadden 7&#160;yard rushing TD. With the win, both Raiders and Chargers reached a 6-6 record, and still stayed behind the Chiefs by 2 games for the division lead. The Raiders also swept the season series from the Chargers for the first time since 2001, and snapped a seven-game losing streak at Qualcomm Stadium. The Raiders were favored by an impeding Chargers offense who struggled to control the game clock and establish a ground game; while the Raiders struggled with penalties and defensive miscues, mostly on the secondary.
Question: How many points did the Chargers trail by at halftime?
Answer: 18