Tactical Evolution of Serve + 1 Sequences in Elite Junior Female Tennis: A Comparison Between U12 and U14 Categories

The Serve + 1 sequence is critical in tennis, yet its tactical evolution during the key U12-to-U14 transition in elite female players remains under-studied. This study used sequence analysis to compare Serve + 1 patterns and characterize the tactical development between these two age groups. This study conducted an exploratory sequence analysis to identify and compare 1298 points from 12 international tournament matches involving a total of 17 unique players, distributed across the elite U12 (n = 9 unique players) and U14 (n = 8 unique players) players. Four-event sequences (Serve Direction > Third-Shot Type > Impact Zone > Bounce Zone) were systematically coded. Data were analyzed using sequence dissimilarity analysis (Hamming distance) and discriminative subsequence analysis. A significant tactical divergence was found on the first serve on the deuce court (Pseudo F = 8.33, p < 0.01; Pseudo R2 = 0.018) and the second serve on the deuce court (Pseudo F = 3.32, p < 0.01; Pseudo R2 = 0.015). U12 players relied on constructive, predictable patterns, favoring wide serves on the first serve (54.3%) and forehands (63.8%). Conversely, U14 players demonstrated offensive patterns, characterized by an immediate return error after a ‘T’ serve (33.7% unreturned serves) and the strategic integration of the backhand (36.9%) on second serves. This transition reflects a fundamental shift from point-building to aggressive, point-ending tactical behaviors. These findings provide an initial, exploratory data-driven framework for sequence-based training aligning with the developmental trajectory of junior female players.