Board Thread:Game Discussion/@comment-9017943-20130801042438/@comment-13248161-20130801121215

It looks to me like when you beat a wave led by an Uncommon foe, you get a Net as a victory reward. If the wave is led by a Rare foe, you do not get a Net. Hence, if you skip capturing the Uncommons you can build up a supply of Nets to take shots at the Rares and higher.