Jumpstart in F1 is when a driver starts the race before the official start signal. This is considered a violation of the rules and can result in a penalty. The penalty can be either a time penalty or a drive-through penalty.
The penalty is given to ensure a fair start for all drivers. During a jumpstart, a driver moves from his grid position before the starting light, which is five red lights, goes off. To measure this, a sensor is used to detect movement on the grid.
Every grid box is equipped with sensors to detect movement. However, there is a tolerance value for this sensor. This tolerance allows the natural movement of the drivers when setting up the car for the race.