Racket sports offer an enjoyable form of physical activity and are fertile ground for interactive technologies supporting new players. Yet, current research has neglected its potential to support not only active players but also coaches in their training methods. To investigate how interactive technologies can support skill acquisition in training, we designed an Electrical Muscle Stimulation (EMS) system that helps maintain the ready position in crossminton. We compared the system with a vibrotactile solution in a user study, interviewing novice players and experienced coaches about their perception of the system. The system allowed coaches to effectively and immediately guide players to the ready position. An EMS-based feedback system for coaches can potentially reduce delay (physical and cognitive) for trainees, as stated by coaches. Our work contributes insights into designing systems that facilitate learning sports techniques using interactive feedback.