You do not need to sign up with a team for a Challenge event (Heavy, Tough, and Basic).
When you sign up for an event you will be put into a class. These events are intended to take each individual person in the class and build that class into one large team. If you are looking to do the event with some buddies (highly recommended) just make sure you are all signed up for the same event.
For Star Course events, you are no longer required to sign up or participate with a team. We do recommend a team of at least one more person since it can be more fun that way but you can absolutely do it solo too!
You can check out all of our events here: https://www.goruckevents.com/