The objective of this study was to investigate the management practices that affect undesirable behaviors in American Quarter Horses (AQH) confined to box stalls. A total of 105 adult AQH, comprising 29 females, 22 intact males, and 54 castrated males, housed in box stalls for at least 30 days, were included in the study. Behavioral activities were recorded through visual inspection at 5-min intervals over a 24-h period by two observers who took turns in shifts of 4 hours. Parameters related to animal characteristics, stall conditions, handling, training, nutrients supplied, and feeding behaviors were considered independent variables, and the time spent in undesirable behaviors was the dependent variable. Data were subjected to exploratory factor analysis and hierarchical cluster analysis. Four principal components were extracted. Two clusters were identified based on the time spent in undesirable behaviors: low-incidence group (25 ± 13 minutes) and high-incidence group (97 ± 52 minutes). Nutritional status (P = .1447), physiological status (P = .1372), and training routine (P = .1160) had no significant effects on the dependent variable; however, the effect of feeding behavior (P = .0444) was significant. A low dry matter intake/requirement ratio (P = .0470) and a high heart rate at rest (P = .0444) indicated that inadequate nutrient supply is a determinant of the time spent in undesirable behaviors in AQH. Aspects related to management practices such as horse nutrition, feeding behaviors, and training routine should be considered to reduce undesirable behaviors in AQH.