Jamie Roberts believes new defence coach Nick Easter deserves more than Harlequins' inconsistent Aviva Premiership opening.
Wales centre Roberts has challenged Quins to shape up after shipping seven tries in their 47-18 defeat at Wasps last weekend.
Roberts insists former England number eight Easter had made a bright start to his coaching career - and one Quins' players have so far failed to match.
Harlequins host Northampton at The Stoop on Saturday, with Roberts insisting boss John Kingston's men now have the perfect chance to prove their Premiership mettle.
"We're doing great things one week, then doing some other things the following week, regressing on some of the things we've done the week before," said Roberts.
"We're not being consistent across our game, but we've got a great opportunity this weekend. Things can turn round very quickly I think.
"At the moment we're less than the sum of our parts, and that needs to change very quickly, and the responsibility's on the players to make that happen.
"Nick Easter's going well, he's started his coaching career very well.
"He sees the game, he's a very clever guy.
"When you speak about defence he's very switched on, he knows the game inside-out.
"He's finding his feet very quickly and all the lads are buying into what he's trying to do with the side.
"It can't be perfect every week and he was very disappointed with Saturday, but he's a very good motivator and a guy all the lads have a lot of respect for.
"He's a very, very good player, I've played against him a number of times.
"He was very disappointed at the weekend and we owe him a performance this weekend."
Quins make four changes to the starting XV that lost to Wasps. Joe Marler, Rob Buchanan and Kyle Sinckler return in the front row while Nick Evans is back from injury at fly-half.
Luther Burrell, Stephen Myler, Tom Wood, Teimana Harrison and Ahsee Tuala will all return to Northampton's line-up for the Harlequins clash.
England prop Ellis Genge will make his first Leicester start at Welford Road when the Tigers host Worcester Warriors on Saturday.
Fly-half Ryan Lamb will start for the Warriors, with England centre Ben Te'o among the replacements.
Wing Charlie Sharples will make his 200th competitive appearance for Gloucester in the west country derby at Exeter.
Luke Cowan-Dickie and Julian Salvi return to the Chiefs' line-up for the Sandy Park clash, with Sam Hill replacing Ollie Devoto at 12 and Henry Slade at 13.
David Wilson will make the first full start of his second Newcastle stint when the Falcons host Bristol at Kingston Park.
Scrum-half Michael Young comes into the starting XV too, while David Lemi will make his first appearance of the season for Bristol after knee trouble.