This paper examines soccer teams' strategic choices about the extent of offense/defense to adopt in competing with other teams. The sample is European Champions League group stage matches played between 1997–1998 and 2009–2010. We begin by developing a characterization of teams' strategies (extent of offense or defense) using principal component analysis. This is used to estimate the relationship between a team's probabilities of scoring and conceding goals and its chosen strategy. Knowing that relationship, it is then possible to derive a team's optimal strategy, and to study how this varies in different situations (such as playing at home or away). A comparison between optimal and actual strategy reveals that teams appear to adopt more defensive strategies than is optimal. A notable feature of our study is that we model a team as choosing a strategy at the start of each match and also at half time, thereby incorporating a dynamic element. (JEL C23, C72, L83, Z00)