# Development and Reliability of a Street Skateboarding Notational Analysis Framework and Application
## 4 Discussion  
A NA system and protocol were designed to capture outcome-impacting aspects of competitive street skateboarding performance and applied it to broadcast footage from the Tokyo Olympics. Overall, intra-rater reliability for the expert rater was good, with no notable differences in reliability across groupings (trick and obstacle types, or time durations). Frame selection and derived temporal feature reliability varied with obstacle types (rails, ledges, quarterpipes) and trick types (grinds/slides, combination/non-combination). Specifically, the reliability of obstacle interaction frames (Frame\({}_{\text{IA-Start}}\), Frame\({}_{\text{IA-End}}\)) and associated performance times (Time\({}_{\text{IA}}\), Time\({}_{\text{TO}}\), Time\({}_{\text{LD}}\)) were the most impacted, with longer durations being less reliable. Overall, the PA approach and associated NA system developed demonstrated acceptable reliability of key TA event frame selection (MAD < 2 frames) by a single, experienced rater. In contrast, inter-rater reliability was considerably lower, albeit better when judged as consistency versus agreement; for example, the lower bounds of total trick attempts and interaction time increased to 0.95 (from 0.65) and 0.69 (from 0.38), respectively, when using a consistency model. Acceptable intra- and inter-rater reliability had been observed in technical sports previously, such as with jump height from 2D video footage of gymnastics vaulting [34]. This might suggest that the extra complexity of the skater-skateboard-obstacle interaction with the inconsistency of broadcast footage potentially impacts reliability. Also, more experience and familiarity with the NA system might improve reliability, with a single, experienced rater being preferable in practice. However, insights can be provided from the inter-rater reliability results as to what specifically may impact a rater's ability to reliably code skateboarding metrics. Building on these observations, a more detailed breakdown of reliability reveals important nuances between frame selection and timing measurements. Take-off and landing frames were more reliably selected than frames influenced by obstacle interaction. Moreover, trick time, derived from take-off to landing, exhibited the highest reliability. A possible explanation is that movements occurring over shorter durations, such as the pop, provide less room for variability in frame selection. The clear definitions and nature of these movements, typically starting from flat or inclined ground, make it easier to distinguish the frame when wheels leave the ground. Thus, temporal features derived from broadcast footage of tricks in the transition should be limited to interaction time, to avoid using unreliable take-off and landing frames. In contrast, identifying the start and end of obstacle interactions, such as with rails or ledges, was less reliable. Initial contact of the board or wheel trucks was visually less distinct, and longer durations between take-off and the obstacle interaction further decreased reliability. This is likely due to more complex movements of the board and skater, such as combination tricks, which tend to be more dynamic and create visually complex scenarios that make pinpointing the start of the obstacle interaction more difficult. These limitations could possibly be mitigated by utilising a 'zoom' feature or higher resolution footage (e.g., sharper videos). Obstacle interaction reliability also decreased with longer interaction times. This relationship appears to be influenced by aspects of trick difficulty and variety. The duration of obstacle interaction often equates to the grind/slide time, and skaters increase this via distance along the obstacle and/or by decreasing speed. Although obstacle length was not controlled, it is postulated that reduced speeds (e.g., increased interaction time) confounded selecting the point of clearing an obstacle.