> ## Documentation Index
> Fetch the complete documentation index at: https://docs.uplift.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Initiation

> The start of the tennis serve.

## Technical Details

* **Variable Type:** Event
* **Data Type:** Integer
* **Units:** Frame number
* **Column Name:** `initiation_event`
* **Required for QA:** False
* **Measurement:** the low point of the non-dominant hand before [Ball Release](/biomechanics/activities/tennis/events/ball-release)

## Description

Initiation marks the very beginning of the serve when the player starts the motion by identifying the low point of the non-dominant hand before ball release.
This event defines the start of the [Preparation](/biomechanics/activities/tennis/overhand_serve#phases) phase and is used for phase duration calculations.

## Use Cases

* Serve phase timing analysis
* Preparation phase duration (initiation to ball release)
* Full serve duration (initiation to termination)