Contests between groups are prone to intra‐group externalities (free‐riding). Yet, costless incentive schemes that entirely avoid free‐riding within a group might be undesirable, both individually and socially. In contests between two groups, a relatively weak (i.e., small or unproductive) group will optimally not implement them because they compound differences in strength between groups. If the groups are of relatively similar strengths, they are both worse off when they rein in their intra‐group externalities compared to a situation where they do not. If groups' strengths differ sufficiently, the relatively strong group benefits at the expense of the relatively weak one. (JEL Z13, D72, N40, D74)