One way a target government can try to mitigate outbidding violence is to increase enforcement efforts to intercept contributions and arrest volunteers to militant groups. We expand the workhorse outbidding model to account for this decision. States with greater enforcement capacity indeed benefit, partially from directly stopping contributions and partially from deterring supporters from making contributions in the first place. The decreased prize therefore also tempers outbidding violence. As a result, competition is contingent on enforcement capacity, with the effect of another group growing larger as that capacity declines. Statistical analysis finds broad empirical support for our mechanism: competitive violence is most pronounced when governments incur higher marginal costs of enforcement. These results increase our confidence that competition drives violence more broadly, as competing explanations do not predict this conditional effect.