The tidal disruption and subsequent accretion of a star by a supermassive black hole can be used as a laboratory to study the physics of relativistic jets. The ngVLA is the only planned instrument that can both discover and characterize a large number of these short-lived radio sources. In particular the high-frequency capabilities of the ngVLA enable this important leap forward. Multi-frequency radio follow-up observations (3 - 100 GHz) of tidal disruption events found in optical or X-ray surveys will provide a measurement of the jet efficiency as a function of black hole spin, thus enabling a direct test of the prediction that relativistic jets require high spin. Hundreds of tidal disruption jets will be discovered in a blind ngVLA survey for radio transients. By including VLBI observations with the ngVLA Long Baseline Array, we can resolve some of these sources, obtaining a robust measurement of the jet launch date and the magnetic field strength. From the thermal emission of the tidal disruption flare we can measure the accretion rate at this launch date, thus providing another unique opportunity to identify the conditions that lead to jet production.
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