All right so I came up with the solution myself, here is what you do: open
Chivalry Medieval Warfare\UDKGame\Config\UDKGame.ini
one of the rows should say something like this:
Bindings=(Name="GBA_Sprint",SecondaryKey=,Command="SprintState true | Onrelease SprintState false | CameraSprint true | Onrelease CameraSprint false",Control=False,Shift=False,Alt=False,bIgnoreCtrl=False,bIgnoreShift=False,bIgnoreAlt=False,Flag=,FriendlyName="Unknown") ```mine is set to have sprint on toggle and bound to middlemouse so I copy paste a line right below this one but change _GBA_Sprint_ to _GBA_Sprintalt_. Since this new command is going to stop sprinting on release I modify my GBA_Sprintalt _Onrelease SprintState_ and _Onrelease CameraSprint_ to **true** . Now I found _Bindings=(Name="LeftShift"_ at the bottom and made _Command="GBA_Sprintalt"_ so that my shift key execute my new sprint command.