Guard is Useful to:
As I mentioned Guard is a skill that is useful to pretty much every player. Some teams rely on it as the most important skill to execute their game plan. The two that spring to mind are Dwarfs and Chaos Dwarfs. For the Longbeards and Blockers on these teams should be taking Guard as their first skill. If they don’t and perhaps select Mighty Blow instead, they will really struggle against the other blocking teams. Guard is also more troublesome for those other teams making it harder for them to get their blocking game going.
The stronger blocking players, Black Orcs, Saurus, Chaos Warriors etc. make good use of Guard later on, they really need to get Block first then perhaps Mighty Blow to help them generate SPP as they are usually slow to skill up. Saurus may not need it so much as there are usually six ST4 players on the team and can get two dice blocks anyway.
Human Blizers, Norse players, Amazon Blitzers, Skaven Blitzers etc. all should consider Guard as their first skill. As much to help their own blocking game as well as disrupting the offence of the other team when they have the ball.
Big Guys also tend to pick Guard as their first skill as they only have strength skills to choose from normally. On doubles they have other skills to be taken.
None of the Elven teams can get strength skills normally, so taking Guard is a good idea for them on doubles rolls. If they don’t take it then they will really struggle in a ruck and will have to really be careful to not get involved in one. Guard will also let them attack ball carriers in cages easier as well, either as a counter to the corners of the cage, or as a boost if the cage corners don’t have Guard.
In the same way high agility players can leap into a cage to attack the ball carrier, stunty players can dodge in to hit the ball carrier. If you have one with Guard then he can dodge in to assist the blitzing team mate, this can turn a two dice against block into a one die block instead, lessening the risk and increasing the success.
For all the blocking teams players who don’t have normal strength skill access then Guard is also probably the most useful choice for them on doubles. Zombies and Skeletons, Ghouls, Werewolves, Human/Norse/Amazon Linemen, Rotters etc.
Skaven can find uses for it on their Linemen. Gutter Runners with Guard can also work in tandem to attack ball carriers deep before they get into a cage, or a thrower sitting deep waiting for a good time to pass.
There are so many situations and times where Guard could come in useful it is hard to list them here. I’m sure after encountering opponents who utilise it well, or having your own players use it in matches, you will soon begin to see its uses.