  Ranking a vector of alternatives on the basis of a series of paired
comparisons is a relevant topic in many instances. A popular example is ranking
contestants in sport tournaments. To this purpose, paired comparison models
such as the Bradley-Terry model are often used. This paper suggests fitting
paired comparison models with a lasso-type procedure that forces contestants
with similar abilities to be classified into the same group. Benefits of the
proposed method are easier interpretation of rankings and a significant
improvement of the quality of predictions with respect to the standard maximum
likelihood fitting. Numerical aspects of the proposed method are discussed in
detail. The methodology is illustrated through ranking of the teams of the
National Football League 2010-2011 and the American College Hockey Men's
Division I 2009-2010.
