看主办方吧。波马有明文规定的

• For the third straight year, participants will have the opportunity to purchase registration insurance at the point of registration. Participants who elected to purchase registration insurance, offered by RegShield, will be able to have entry fees refunded for multiple reasons including loss of job, pregnancy, illness, and injury. Refunds may only be eligible for those who purchase the insurance policy at the point of registration.
• Entries in the Boston Marathon cannot be transferred, deferred to a future year, and only those who elect to purchase registration insurance may be eligible for refunds.