> ## 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.

# Ball Contact

> The estimated timing of ball contact -  determined by audio signal (primary) or swing through event  (secondary, if ball contact not detected or detected outside of foot contact  and end twist events).

## Technical Details

* **Variable Type:** Event
* **Data Type:** Integer
* **Units:** Frame number
* **Column Name:** `ball_contact_frame`
* **Required for QA:** True
* **Primary Detection:** Audio signal analysis
* **Secondary Detection:** Swing through event
* **Validation:** Audio-based ball contact must occur between foot contact and end twist events.
  If not, uses swing through event (when the rear wrist passes in front of the lead wrist).

## Description

Ball contact represents the instant when the bat makes contact with the ball.
This is detected primarily through audio analysis, using a model to identify the hit "crack".

The secondary detection method ([Swing Through](/biomechanics/activities/baseball/hitting/events/swing-through)) is useful for capturing environment where other athletes are hitting.
Audio-based ball contact detection could pick up other nearby hitters nearby.

## Use Cases

* Largely determines body and bat metrics at ball contact
* Swing sequence completion
* Must occur in correct sequence, otherwise fails QA.