When a group of ladies all share a passion for the same activity and form a close connection as a result. This "sisterhood" may include token males, but they are less likely be welcome to be homantic with the ladies, as this would risk continuing to be welcome in the homance.
The woman and the dude in that van doing this years Ragnar Relay Race sure seem to be close to each other. They cheer for one another, sleep on each other, and smack each others ass after each leg. It seems like they are definitely caught in a bad ass homance.