@jonas, thank you for posting your question. Sorry I haven't gotten to your last email (will respond directly to you as well).
All XPRIZE competitors are required to compete under a legal entity with insurance. XPRIZE requires a team to have a legal entity to ensure we only deal with one entity on all legal matters, including awarding a prize check. An individual competing completely on his/her own does not need to form a legal entity because an individual is considered a legal entity already.
Every XPRIZE also requires a specified level of insurance coverage. This is necessary to protect our competitors and the XPRIZE Foundation. Individual health insurance is not sufficient. As every XPRIZE competition has different insurance requirements, official details can be found in the Competitor Agreement - the legal contract governing the competition.