Denny Hamlin has been penalised 75 points and his crew chief fined and suspended as a result of a rules violation on the #11 Joe Gibbs Racing car at last weekend's Brickyard 400 Sprint Cup Series race at Indianapolis Motor Speedway.

NASCAR confiscated several rear firewall block-off plates after the finish of Sunday's race in which Hamlin finished in third place having started in 27th position. The items were taken to NASCAR's Research and Development Center in Concord, North Carolina, and on Tuesday the sanctioning body announced that it had found the plates to be in violation of numerous sections of the Sprint Cup rule book.

The plates are part of the Cup car's driver protection as they help prevent fluids, fumes or flames from breaching the driver area and there are firm rules on what the plates can be made from and what size they can be. It appears that these were left open in Hamlin's car, with the airflow potentially helping to increase downforce on the car leading to a significant performance advantage.

Several cars had left the covers loose in the run-up to Sunday's race until NASCAR clamped down as it helps team members make modifications to the car's set-up during practice. It appears that all the plates in other cars were sufficiently tightened up after the warning except for the #11.

As a result, NASCAR ruled that the #11 had breached sections 20-2.1 K and 20-2.1 L, 20-3.4 and 20.3.5 of the rules covering the car body work - specifically the sealing and securing of all sheet metal and firewalls - as well as section 12-1 which pertains to actions detrimental to stock car racing. The violation was deemed serious enough to warrant a P5-level penalty under NASCAR's new system of dealing with infractions introduced at the start of 2014.

"P5 penalties, in general, are extremely serious," states the rule book. "They represent other key safety areas ... and potentially performance-related areas of the car that might or might not afford a competition advantage, but with a violation occurring in such a fashion that it would be naive to attribute the violation to an accident, omission, or misunderstanding, even if it was [the case.]"

A P5 penalty mandates a loss of 50 driver and car owner points and a fine starting from $75,000 plus a six-race suspension for the crew chief. The fact that the infraction wasn't discovered until post-race scrutineering means that further penalties become applicable.

In this case, NASCAR have determined a 75 point driver and owner championship point deduction and a fine for Hamlin's crew chief Darian Grubb of $125,000. Grubb is also suspended for the next six championship races, meaning that he cannot be present at any venue during a NASCAR-sanctioned event. Grubb will also be on probation for the next six months.

The car chief of the #11, Wesley Sherrill, has also been suspended for six races and placed on probation for six months.

Even though the penalties are the heaviest imposed so far this year under the new system - no one has yet received a penalty from the highest level, P6 - they do not deal as heavy a blow to Hamlin's championship hopes as they might otherwise have done.

Under the new system for making the play-offs, Hamlin has a fairly secure hold on a Chase spot thanks to his win earlier this year at Talladega. As long as he finishes in the top 30 in the points and continues to attempt qualifying in the remaining six races before the Chase cut-off in September he will almost certainly still be one of the 16 drivers left in the running for the title.

With the points deduction announced on Tuesday, Hamlin drops from 11th place to 21st in the driver championship points. In the past that would have been a devastating blow to his chances of making the Chase, but now the emphasis is on wins it proves to be relatively harmless as Hamlin is still ahead of two other Chase hopefuls with a win apiece, Aric Almirola and Kurt Busch.

Grubb will still be able to return to duty for the first race of the Chase at Chicagoland on September 14 provided that he starts serving the six race suspension without delay instead of continuing to work subject to appeal. To that end, Joe Gibbs Racing have announced that Grubb will go on suspension with immediate effect - even though the team has confirmed that it does indeed plan to appeal the penalty.

"Joe Gibbs Racing (JGR) is aware of the penalty issued by NASCAR today regarding the #11 team's post-race inspection infraction following Sunday's Sprint Cup Series race in Indianapolis," the team said in a brief statement after the penalty was announced. "JGR will plan to appeal the penalty, however, crew chief Darian Grubb and car chief Wesley Sherrill will begin to serve their suspensions starting this weekend in Pocono."

The appeal will be heard before a three-person National Motorsports Appeals Panel at a date to be confirmed. The burden of proof rests with NASCAR, and if the sanctioning body loses then it cannot appeal whereas if JGR were to lose then they could take the case to the new Final Appeals Officer, Bryan Moss, whose decision is final. All fines collected go to charitable causes.

As a matter of routine, NASCAR also took the race-winning Hendrick Motorsports #24 Chevrolet of Jeff Gordon and the #18 Toyota of Hamlin's team mate and race runner-up Kyle Busch back to the R&D Center for post-race evaluation. No issues were reported on either car.