Everyone wants to see the home runs. But right now, mostly what the Lions are getting with their defensive front are doubles. Double teams, that is. Extra protection from opponents trying to keep the Lions’ four-man pass rush — the well-advertised strength of their defense — at arm’s length. “I know why they’re doubling us,” said defensive coordinator Gunther Cunningham, who spent a good deal of his time during the bye week trying to figure out how to turn those extra-base hits into grand slams. “They don’t want us to hit the quarterback. And my God, you need a Sherman tank to get through all the guys they hold in to block sometimes.” Luckily for the Lions, they have one in Ndamukong Suh, a one-man wrecking crew who is taking on double teams — “I mean, there isn’t a play I can remember where he’s single-blocked” — and making a case for NFL defensive MVP honors this season. But if the Lions are going to make a serious bid for the playoffs, starting with Sunday’s matchup of division leaders in Chicago, they know they’ll need more from their front four in the second half.