A sport that is making many older Americans more active could be backfiring for health insurance companies, according to UBS. Pickleball is a tennis-adjacent sport that has exploded in popularity since the Covid-19 pandemic, attracting millions of new players and celebrity investors. But UBS analyst Andrew Mok said in a note to clients Monday that the sport’s growth and popularity among seniors could contribute to rising health-care spending. “After analyzing the growth in pickleball as well as the nature and frequency of related injuries, we conducted a bottom-up analysis of medical costs. In total, we estimate $250-500 mn of medical costs directly attributable to pickleball and see potential for greater medical costs indirectly linked to pickleball,” the note said. Insurance companies may be providing some circumstantial evidence for Mok’s theory. UnitedHealth executives warned during a Goldman Sachs conference on June 13 that the company was seeing higher-than-expected health-care utilization, particularly in outpatient settings. Mok pointed out that pickleball could be one of the factors causing that increase. “We estimate that 80% of the cost is treated in outpatient settings (ie ED, Doctor Visits, OP surgeries) and 85% accrues to Medicare, which coincides with higher trend categories called out by UNH and HUM . All said, we estimate that pickleball medical costs could be driving 5-10% of the unexpected medical cost trend this year,” the note said. The update from UnitedHealth weighed on the insurance stock , and shares of UnitedHealth were still down more than 3% from June 12 at Friday’s close. — CNBC’s Michael Bloom contributed reporting.