Rotation is one of the largest uncertainties in our understanding of low-mass stars. As stars transition from the main sequence onto the red giant branch, their structures change significantly, with expanding cores and contracting envelopes. These simultaneous changes mean that measurements of the rotation rates of their interiors are excellent probes of the rate and mechanism of angular momentum transport, and therefore give us a new way to probe the physics of rotation. Using asteroseismology, we have measured the interior rotation rates of these transitioning subgiant stars using data from the NASA TESS mission. I will discuss how these measurements compare to theoretical expectations and previous results, as well as the broader implications of these kinds of careful analyses for our understanding of complex stellar physics.