The Registration cut off date may need to be set to prevent this. 
  1. Navigate to Fundraising > TeamRaiser
  2. Enter the name of the event
  3. Click Search
  4. Click Edit under the Actions column
  5. On the Identify TeamRaiser step, scroll to step 5 event date (or, for virtual events, when registration closes)
  6. Update the date
  7. Click Next
  8. Click Publish in the left navigation
  9. Click Finish