Which phase comes right after the reaction time in sprinting?

In sprinting, the phase that comes immediately after the reaction time is the drive phase. The sequence of a sprint race is:

1. Reaction time - the interval between the starter's gun and the sprinter's first movement out of the blocks. This is a purely neurological response, not a movement phase.
2. Drive phase (also called the acceleration phase) - the sprinter pushes explosively out of the starting blocks, maintaining a low body angle (approximately 45 degrees) and driving powerfully with the legs. Each stride during this phase increases the sprinter's velocity. The drive phase typically lasts for the first 30-50 metres of a 100-metre race.
3. Maximum velocity phase - the sprinter reaches and maintains top speed with an upright body position.
4. Deceleration/finish phase - the sprinter's speed begins to decrease slightly in the final metres as fatigue sets in, and the athlete leans at the finish line.

There is no "relaxation phase" as a formal phase of sprinting. While sprinters must keep their upper body relaxed during the race to avoid wasting energy, this is a technique cue, not a named phase.