Understanding tactical behaviour in invasion sports has historically been limited by reductionist approaches that pay little attention to the complex interactions that occur within the performance context. For example, much of the published research has focused on 1v1 dyadic relationships such as those between the ball carrier and their immediate opponent. In an attempt to understand tactical behaviour in a more holistic manner, recent research trends have adopted ecological, systematic approaches. These approaches capture the importance of the relationship between the individual and their wider performance environment. At present, there still remains a lack of research specifically looking at tactical behaviour in netball. As a sport, netball offers a unique context to explore tactical behaviour due to the various rule-based constraints placed on the athletes. For example, when a netball player is in possession of the ball they cannot move (more than one step), and they must pass the ball within three seconds of receiving it. In addition, defensive players are restricted by the obstruction and contact rules which dictate how players are able to gain possession of the ball. As a result, the tactical behaviours that netballers use to reach performance goals (i.e., maintain possession and score on attack, or create turnovers and prevent scoring on defence) require strong interpersonal relationships. This thesis is comprised of three empirical studies which have been developed to better define, identify and assess tactical behaviour in netball. The first study (chapter four), adopted the Delphi method to capture expert coach knowledge and create a well-defined, concise list of tactical behaviour definitions specific to netball. The Delphi method consisted of three rounds of data collection, which began with interviewing twelve expert coaches to answer the question; why do turnovers occur in netball? The coaches’ responses were thematically analysed and developed into a preliminary list of tactical behaviour definitions. In the subsequent rounds of data collection, the coaches rated their agreement to the definitions, and were able to provide amendments if necessary. As a result, a list of 18 tactical behaviour definitions were developed to form the Tactical Principles Guideline (TPG). Interestingly, the majority of the tactical behaviours identified by the coaches could be considered as ‘off-the-ball’ behaviours such as; protecting space and decisive movement on attack, as well as confusing space and dictating movement on defence. The second study (chapter five), was conducted to further validate the tactical behaviours within the TPG. This validation process was conducted to ensure that a different group of coaches were able to identify the tactical behaviours in a variety of turnover scenarios. In this study, a group of coaches were instructed to use the TPG to identify the different tactical behaviours they observed, as well as identifying which players were involved in creating and causing the turnovers. The results highlighted that all of the tactical behaviours were considered identifiable, meaning that the TPG can be used to explain why turnovers occur in netball. In addition, the tactical behaviours that were most frequently identified were behaviours that occur off-the-ball, such as; options to the ball, decisive movement, dictate movement, and defensive unity. The coaches also identified an average of 4.86 defensive players involved in creating each turnover, and an average of 3.96 attacking players involved in causing each turnover. These findings emphasise the vital role that ‘off-ball’ players have in creating and causing turnovers in netball. The final study in chapter six was conducted to test the applicability of the TPG in a real context for team selection. During a development camp, a group of coaches and selectors used the TPG to rate 49 athletes. These ratings were analysed to determine if the coaches and selectors ratings were able to distinguish between the athletes who were selected and those who were not selected into a national squad. The results suggest that the selectors ratings could distinguish between selected and non-selected athletes, however, the coaches ratings could not. A justification behind the differences between selectors and coaches is potentially due to the different underlying purpose for the rating task. For the selectors, the ratings were conducted to aid in their team selections, however, for the coaches, the assessments were conducted to provide the athletes with feedback about their future development. Therefore, as team selection requires positions (shooters, mid-courters and defenders) to be filled, it is not necessarily the ‘best’ players (who would theoretically have the highest ratings) that get selected. In summary, an important outcome of the research in this thesis, was the identification of the key tactical behaviours that are used to create or cause turnovers in netball. In particular, the emphasis placed on off-the-ball behaviours contributed new and novel research to capture a holistic understanding of tactical behaviour in netball. This research has produced a guideline for defining, identifying and assessing tactical behaviour in netball which is theory-based and practically endorsed by those coaches and selectors who have had experience with using the TPG.