Coaches’ motivating style plays a key role in athletes’ motivational outcomes. However, limited research has explored the effects of athletes’ perceptions of coaches’ need-supportive and controlling styles on the bright and dark motivational pathways in the sport setting, and particularly in young water polo players, where one out of two players drops out of this sport as adults. Guided by self-determination theory, the objective of this study was to analyse the differentiated effects between water polo players’ perception of need-supportive and controlling style from their coaches on their reported basic psychological need satisfaction and frustration, motivation and sport commitment. In this cross-sectional study, 633 Spanish water polo players (33.96% women; Mage = 14.74), from 43 clubs and three age groups (U-14, U-16 and U-18) completed validated questionnaires assessing study variables. Structural equation modelling showed a positive association of players’ perceptions of need-supportive style from their coaches with their reported need satisfaction, autonomous motivation and sport commitment. Similarly, perceived controlling coaching style was positively associated with reported need frustration, controlled motivation and amotivation. Regarding cross-paths, perceived need-supportive coaching style was negatively related to reported need frustration, while reported amotivation was negatively associated with reported sport commitment. These findings suggest the importance of water polo players’ perceptions of (de)motivating styles from their coaches on their reported motivational outcomes and sport commitment. Players’ perception of coach need-supportive behaviours and, in particular, the avoidance of perceived controlling behaviours, buffer against experiences of reported need frustration and, consequently, amotivation, which seems to play a key role in preventing lack of sport commitment in young water polo players.