Worst Case Allocation is the total amount of memory of your VM when all VMs in the cluster consume their full amount of allocated resources or when overcommitment happens this is what amount of memory that VM can get. It might includes memory overhead that's why it is larger than configured memory. You can go with below links for more understandin.
https://www.google.com/amp/s/vmguru.com/2013/04/vsphere-5-memory-management-explained-part-1/amp/