The purpose of this study was to investigate differences in the patterns of supine spontaneous leg movements produced before sitting onset between infants with typical development (TD) and infants at risk for developmental delay (AR). In this cross-sectional, observational study, 35 infants were included; 18 infants with TD (130.4 ± 38.0 days) and 17 infants AR (124.1 ± 65.7 days). Infants were placed in the supine position and video taped for four to five minutes while in an alert, content state. After the recording, videos were coded frame by frame to identify the type of each leg movement produced: single flexion, single extension, alternate flexion, alternate extension, parallel flexion, parallel extension, leg wave, leg circle, leg thump, foot rub, foot flexion, or foot rotation. Unilateral movements (single flexion and single extension) were the most common leg movements in the TD group. Infants in the AR group produced a significantly lower proportion of unilateral and foot rub movements than infants with TD. These results provide a foundation of the types of leg movement pattern differences to build on in future research. Knowledge about differences in spontaneous movement patterns between infants in the AR group and infants with TD has relevance both for early identification of neuromotor impairment and clinical practice.