I’ve mostly explained about saving rerolls and not using them; so when should you use your rerolls? The most common use for rerolls would be when blocking, there is no skill in the game that lets you specifically reroll block dice (Pro will half the time, but nothing in the guise of Dodge etc.). Even if you are blocking with your block players, on average every thirty sixth block you will roll double skull. This is a great time to have a reroll handy, especially if it is your first action of the turn. So you can see in these spots if you had used all your rerolls already, your player goes down and you lose out on a whole turn. A two dice block without block will cause you to use a reroll around eleven percent of the time as well.
The other times is it handy to have a reroll is when you get a chance to hit the opposing ball carrier. If you have a two dice hit on him, depending on the players skills you will have a good chance of knocking the ball carrier over. One dice hits are more risky to reroll and may require more consideration rather than an automatic use. It is more situational as to if you want to reroll those, if it is near the end of the drive and you can’t get any more cover near by, then go ahead. If it is at the start of the drive and the rest of your team is in a good position, you may elect to save the reroll rather than risk rolling a skull and look to hit them again next turn. Perhaps you failed the dodge roll to go and blitz the ball carrier, again this may be a good spot to reroll.
The other side of the ball is when you may need to reroll a dodge or go for it to make sure the ball is secure, this may be either to complete a cage or to run out of blitzing distance from the other team.
Reroll Safety Net:
The other great benefit of having rerolls is the so called safety net that they provide. Any of your players can attempt any dice roll in the knowledge that you can have two attempts at it. Obviously this will disappear for the remainder of any turn once you have used a reroll in it. For example you are playing with Humans and facing a Dwarf team. You managed to break through his line and run the ball carrier through with a couple of players to defend him. Now you have some of your Linemen being marked up by Dwarf Longbeards. They have AG3 so they will succeed at dodging more often than not into an unmarked square. The Dwarf player has Block, so a once die block will suit them more than you, especially given their high Armour and Thick Skull. They are also really slow and can be outrun. With a reroll in hand you may elect to start dodging your Linemen away into a position to better assist the defence of the ball. If you fail one you can reroll it and hopefully succeed. If you succeed anyway you can try the same with your next player. These are the kind of actions you can safely attempt with a reroll in hand. Your opponent may also start cursing your good luck for those times when you pass every single roll and have no need for the reroll at all. If you have perhaps four to dodge away and the first three succeed fine, you may decide to let the last one fall over and save the reroll as well.
So as you can see there are quite a few things to consider when it comes to using your rerolls. The less you have the more careful you should be in regards to using them. The less turns there are in relation to how many rerolls you have can dictate how freely you can take a semi risky action towards the end of your turns, those one die blocks or non Dodge skill dodges for example. If you have one reroll left per turn left then it makes sense to go ahead and try them. Use your rerolls wisely and it may give you that extra edge you need to win.