Those of us who play Muslims post a lot about flanking, but say precious little about what's doing the pinning while all this flanking is going on.
This gives the impression that fighting with Muslim units is more difficult but no more effective than teching-up and bashing into things with Catholic armored units.
Rather than make up some rules for fighting as Muslims, here's a observation on Muslim archer units. Tell people the differences, and let them design their own tactics.
Hopefully, this will be the first of several such tips from a variety of experienced players on using Muslims
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Look at the melee stats for Catholic infantry, and then for archers. You will find a large divide, a clear division of labor. Catholic swords and spearmen are clearly meant to do the fighting. Archers are clearly restricted to a supporting role. There are exceptions -- handgunners are arguably better melee troops than missile ones -- but that's the rule of thumb.
You won't find the same clear division in Muslim armies. Turkish Futtawa, for instance, are better melee units than Arab Infantry. Almohad Murabitan javelin troops can at least hold their own for a while against vanilla urban militia, and have much better morale. They can whip peasants, Slav Warriors and similar low-value units. Even the lowly Desert Archer has much better melee stats than vanilla archers, and better morale.
So, you should stop firing arrows and charge? No, but your greater melee option does mean that when a melee opportunity unexpectedly opens up in front of you, perhaps you should take it. Suppose a friendly melee unit is routed and the pursuing unit is strung out in the chase. Your Futawwas should charge. A dangerous opening in your line could become a rout for the other side.
Muslims can also be a more daring with their archer units. They don't have to worry so much about an isolated archer unit getting killed by hobilars, for instance. Catholic archers have to stay behind line infantry or be escorted by cavalry. Muslim units don't, or are at least less dependent on protection. They can skirmish farther out in front of the battle line and then pull back to the sides when the melee units become engaged, which takes away their enemy's shield bonus.