A mix of math, programming, and sports.
Graphs are a mathematical objects which describe a set of things and the relationships between them. Using a graph, distances between teams are determined which are then used to find create team ratings.
In sports the outcome of the game is not the same every time teams play, there is some inherent randomness in the game. This randomness puts an upper limit on the accuracy of predictions, and understanding it is important for evaluating sport models.