From a weapon simulation perspective (and assuming that the sim persective has something useful to say here), delay with the express intention of baiting your opponent into leaving themselves open during an attack, is a good tactic except in these two situations. (There may be more, but it is definitely a bad idea in the two situations.):
1. Your opponent is more skilled than you. They will use the fact of you ceding the initiative to launch a series of feints and attacks that you will be hard pressed to counter. Plus, they
know that you intend to block and counter-attack, and will take that information into account. A feint is defined as, "any move that gets your opponent to do something predictable which you can then act upon." When you cede initiative to a superior opponent, you basically granted them a free feint.
2. Your opponent is less skilled than you, but either doesn't know, doesn't care, or is just plain unpredictable. They do something off the wall, catch you by surprise, and you end up in a bad position. This is low percentage for your opponent, but it can happen.
In game terms, this sounds like invoking relative weapon skills in some fashion, which I would think would have several reasonable options in Runequest II. You could, for example, simply rule that if both attack simultaneously, and both get the same level of success (both hit, or both crit), then the one with the higher roll is the only one that can parry. All other rules still apply.
So the guy with a 2H weapon can't parry either way. But if he rolls better than the weapon+shield guy, then he sneaks his attack in before the shield can be brought into play. We are talking fraction of a second on reation time. The weapon+shield guy is moving his shield to block, but it doesn't get to the right place in time. On the other hand, if the weapon+shield guy gets the better roll, then he gets to take maximum advantage of his equipment and pulls off the bait and counter.
That covers the two situations that I mentioned, since the lesser skilled opponent with 2 weapons will occasionally get in a nasty unparried lick, but more often than not will be frustated. This leaves bait and counter as a viable tactic, but one with some risk, especially if you haven't assessed the opponent correctly
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