FORFEND ... ENTER & END

Steelheads have Forfend, a nice little ability that causes headaches in the rules forum.

Forfend has two requiremenst: enter melee range and end movement in melee range. You have to do both to trigger the attack. If you move your steelheads forward to engage enemy models, and those model then just end their movement, they only satisfied one of the two requirements, therefore, no forfend attack.

...and...

Sadly, Shadowshift DOES NOT trigger Forfend.

Forfend triggers when an enemy model moves into and ends its movement within a Steelhead's melee range. Ends movement has been shorthand for a VERY long time to indicate "Ends the movement portion of the model's activation." Shadowshifts will not trigger Forfend, or Defensive Strike, sadly.