The skid block is a plank that runs the length of the underside of the car. It has to be a certain thickness and Jarno’s was deemed to be too worn.

The FIA statement read, The Stewards of the Meeting received a report from the Technical Delegate, stating that car number 11 (Jarno Trulli) did not comply with Article 3.13.1(d) of the 2001 FIA Technical Regulations.
Having heard representations from the Team Representative, the Stewards of the Meeting decided to exclude the car from the Official Race Classification.

Expanding on the statement, FIA technical delegate Jo Bauer said, "having checked the skid block from car number 11 the thickness around the rear hole was measured and found to be 7.5mm, 1.5mm below the minimum required by Article 3.13.d. This high wear is very likely to be caused by the loss of two fasteners which are normally flush with the surface of the skid block. These fasteners are designed to prevent such high wear."

Jordan has announced that they will be appealing the FIA's decision saying, Jordan Grand Prix will be appealing against the decision of the Stewards of the Meeting, to exclude car number 11 (Jarno Trulli) from the Official Race Classification of the United States Grand Prix.
No further comment will be made at this time.
The last time Stewards excluded a competitor on these grounds was in 1994 at Spa with Benetton’s Michael Schumacher.

Jarno has had an incredible run of bad luck since he joined the Irish team at the beginning of 2000. The amount of points he has lost through technical gremlins striking at exactly the wrong time, or being pushed off the circuit through no fault of his own is so large it would be difficult to calculate.

His fourth place at Indianapolis gave the Italian his first points finish in seven races, moving himself into a tie with Jacques Villeneuve and Nick Heidfeld in the drivers' standings and, more importantly, taking Jordan clear of British American Racing in the constructor's table.