Run a test on location ahead of the event and watch the live stream. If it's not playing smoothly it may be that your OBS video settings are too high for the internet bandwidth.
Make sure you test with your actual camera(s) feed, not blank screen or slideshow.
Find out your Upload Speed by visiting or

Configure your OBS Studio Optimal Settings

Open settings in OBS Studio

Output Tab

OBS Output Tab settings

Bitrate: 2000-3000 Kpbs (Make sure it's below your Upload speed)
Keyframe Interval: 2

If your computer is struggling to keep up with video encoding use these settings:
CPU Usage Preset: veryfast (or higher)
Tune: zerotolerance

Video Tab

OBS Video Tab Settings for EventLive

Output Scaled Resolution: 1280x720
Common FPS Values: 30

Advanced Tab

If your upload speed is lower than suggested bitrate, or if it's unstable, make sure to use Dynamic Bitrate.

OBS Advanced Dynamic Bitrate

Checking status bar

Check the status bar while streaming to ensure encoding and streaming are correctly configured.

Healthy OBS Studio Status Bar (located in the bottom part of the window)

Encoding overloaded error

Dropped frames indicator and insufficient encoding speed (FPS below 30).