Though substantial research has been conducted to examine athletes' regulation of their own emotions, recent researchers have begun to study interpersonal emotion regulation (IER), wherein individuals attempt to influence others' emotions. Sport studies have revealed that athletes use various IER strategies (e.g., humour, distraction, positive feedback) toward their teammates, and the use of IER between teammates can relate to important motivational and affective outcomes for athletes. Despite the evidence demonstrating the relevance of IER for athletes, researchers to date have rarely explored coaches' IER toward athletes. Given that coaches play a key role in their athletes' emotional experiences, coaches' IER warrants more investigation. The current mixed-method study examined coaches' beliefs regarding athletes' emotions and their engagement in affect-improving and affect-worsening IER toward their athletes. Competitive level coaches (Mage = 44.0 ± 13.2 years) completed quantitative surveys (N = 208) and participated in semi-structured individual interviews (N = 10). The coaches believed that pleasant and unpleasant emotions can both lead to beneficial or detrimental outcomes, and coaches frequently used affect-improving IER toward their athletes. Though most coaches opposed the idea of deliberately worsening athletes' emotions, some coaches asserted that sometimes it was necessary to downregulate overly pleasant emotions and that providing feedback to athletes could unintentionally worsen their emotions. Coaches also carefully considered athletes' individual differences when engaging in IER. The current findings highlight the relevance of coaches' IER for athletes and suggest useful considerations for coaches and coach education programs.