If a farmer unknowingly plants Monsanto seed because another farmer sold it to him. The purchaser can sue the seller for damages just like any other business. It has everything to do with contracts because the only people getting sued are the ones that have enough seed to plant a second crop. That second crop came from a farmer who signed a contract saying they wouldn't grow seed crops or resell their seed. So someone in the chain broke their contract trying to undercut Monsanto business.