Coach verbal encouragement improves mood state and sustains consistently higher levels of effort, but does not positively affect overall tennis performance: a crossover study

Purpose Sports performance does not reside solely in physical, technical, and psychological preparation. It can also be influenced by external motivation. To examine the immediate effects of coach verbal encouragement on young tennis players’ mood state, perceived exertion, and match performance. Methods Ten young tennis players (aged 9.10±0.99 years) completed the match protocol in a randomised crossover. On separate days, coaches provided verbal encouragement during all eight match games and a non-encouragement condition. Rate of perceived exertion (RPE) and total mood disorder (TMD) scores were collected before and after the match, while RPE was collected after each game. Successful ball scores were also collected. Results TMD scores post-competition were significantly lower in the verbal-encouragement condition compared to both non-encouragement (<i>p</i> = 0.014, <i>d</i> = 0.93, moderate) and baseline conditions (<i>p</i> < 0.001, <i>d</i> = 1.44, large). RPE was significantly higher (<i>p</i>: 0.001–0.009, <i>d</i>: 0.61–2.58, moderate-large) in the ‘encouragement’ condition for 50% of the games (e.g., 2nd–4th– 6th–7th games) and demonstrated a more stable progression throughout the match, with inflection points identified during the 3rd (<i>p</i> = 0.007, <i>d</i> = 1.19, large) and 7th games (<i>p</i> = 0.001, <i>d</i> = 2.63, large), representing distinct phases of effort intensification. Despite improvements in psychology and effort, successful ball scores showed no significant interaction between en-couragement and time factors (<i>p</i> = 0.401, ϗp<sup>2</sup> = 0.11, trivial, ω = 0.42). Conclusions Acute verbal encouragement from a coach enhances mood states and sustains higher, more stable effort throughout match play in young tennis players. However, these psychological and effort benefits do not translate into immediate performance improvements in successful ball scores.