|Model building in game sports should maintain the constitutive
feature of this group of sports, the dynamic interaction process between
the two parties. For single net/wall games relative phase is suggested
to describe the positional interaction between the two players. 30
baseline rallies in tennis were examined and relative phase was calculated
by Hilbert transform from the two time-series of lateral displacement
and trajectory in the court respectively. Results showed that relative
phase indicates some aspects of the tactical interaction in tennis.
At a more abstract level the interaction between two teams in handball
was studied by examining the relationship of the two scoring processes.
Each process can be conceived as a random walk. Moving averages of
the scoring probabilities indicate something like a momentary strength.
A moving correlation (length = 20 ball possessions) describes the
momentary relationship between the teams' strength. Evidence was found
that this correlation is heavily time-dependent, in almost every single
game among the 40 examined ones we found phases with a significant
positive as well as significant negative relationship. This underlines
the importance of a dynamic view on the interaction in these games.
WORDS: Game sports, model-building, relative phase, random walks.