RB Theo Riddick (+4.9) - Riddick has played a pretty limited number of snaps so far this season, but he's certainly made the most of them given that he has the Lions' top offensive grade on PFF. Riddick's actual stats don't necessarily jump out at you -- he has 12 carries for 33 yards and 13 catches for 149 yards and two touchdowns -- but again, that's really due to his small workload more than anything. Of course, the flip side is that Riddick's small sample size means that he hasn't had nearly as many chances to make mistakes as other players, but he's looked quite good when he's actually been on the field.
WR Calvin Johnson (+3.8) - Despite missing the last three games and not being healthy since Week 3, Johnson has the Lions' second-best offensive grade. On the one hand, Johnson, like Riddick, hasn't had a chance to make a ton of mistakes given his lack of playing time as of late, but the fact that he's got the second-best grade on offense despite missing so much time says a lot about just how many struggles this unit has endured so far this season.
RB Reggie Bush (+2.0) - Bush has played in six games so far this season, and he's rushed for 171 yards and one touchdown on 49 carries, which is good for a 3.5 average. He also has 25 catches for 164 yards. While watching games live, Bush has seemingly been outperformed at running back by Joique Bell, but Bell actually has an overall grade of -5.2 right now.
(Note: Riley Reiff was actually the Lions' top offensive player going into Sunday with a grade of +5.7 through seven weeks, but he managed to completely undo that with a -5.8 in London. Ouch.)
LB DeAndre Levy (+15.7) - Levy is currently second overall among 4-3 outside linebackers. Only Von Miller has a higher grade than him, so it's no surprise he's the Lions' top defensive player. Through eight weeks, Levy has 75 tackles, half a sack, one safety, three pass defenses and one interception, and he's played a big role in the Lions' transformation into one of the best defensive teams in the NFL.
DT Ndamukong Suh (+15.6) - Just behind Levy is Suh, who is ranked fourth overall at defensive tackle. He has 23 tackles, 3.5 sacks and one pass defense through eight games, and he kept his play at a pretty consistently high level throughout the entire first half of the season.
DT Nick Fairley (+10.8) - Fairley is the 10th-ranked defensive tackle on PFF right now. He recorded 14 tackles, 1.0 sack and one forced fumble in the first half of the season, and along with Suh, he's helped form perhaps the most dominant defensive tackle duo in all of the NFL.
P Sam Martin (+21.8) - Martin has been excellent this season on both punts and kickoffs. He's got the second-highest grade in the NFL for punts, and he's third on kickoffs. Statistically speaking, Martin is averaging 47.6 yards a punt (with a net average of 41.4), and 27 of his 35 kickoffs have gone for touchbacks. He has been an extremely valuable weapon in multiple areas on special teams.
For more great stats, be sure to check out Pro Football Focus.