Lateral movements of the leg and foot were filmed from behind to evaluate court shoes. Inversion/eversion may be an indicator of potential injuries, but estimates of actual inversion/eversion have typically been measured as the angular displacement of marker pairs on the lower leg and on the shoe. The purpose of this study was to measure the shoe movement versus the heel movement inside the shoe in order to determine the appropriateness of using shoe markers to represent the heel position. Two windows were cut into the heel counter of the shoe to show the heel position in addition to shoe position. The subjects were filmed from behind during a lateral side-stepping movement. The difference between the shoe and heel position was [corrected] statistically significant. The average maximum change in heel inversion inside the shoe was 13.3 +/- 3.8 degrees, compared with 30.7 +/- 6.2 degrees for the shoe. In addition, the maximum change in heel inversion in a barefoot movement was 10.1 +/- 3.1 degrees. The results suggest that for a lateral movement shoe markers do not accurately represent the position of the heel, and heel movement inside a shoe is similar to a barefoot movement. Skin markers on the heel as observed through windows in the shoe give a better indication of the actual position of the calcaneus than do markers placed directly on the shoe.