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i was playing with a friend the other day. He has a nice blue deck. I have a red deck. A few nice creatures came into play, and i had some nice player life point damage going around and then it came down to some of my creatures making damage combinations and i was gearing up for the last few turns to finish it off until....
Horseshoe crab came on the sence. I thought no biggy. I'll kill it or it can only block one creature and move on. However my friend used horseshoe crab in a very powerful way. I came on with a few 2/3, 1/1, 2/2 creatures. my friend used horseshoe crab multi times durring combat. I thought this odd but went with it anyway. I inevitably lost the match due to not being able to move past horseshoe crab during one turn.
I'm raising the question...
can a creature block mulit creatures even during combat (given horseshoe crabs ability to tap one mana to untab horseshoe crab). I ask cause damage is usually the last or second to last step of combat. How can a creature block mulitple times, when damage a creater gives or recives is nearly the last step of combat and choosing blockers is the third step to combat? It would seem that is not correct by theory of the combat sequence.
can an ability be used mulit times during a turn or even during a specific step to either block or give damage mulitple times? The scope of the ability seems far removed from its mana cost and commonaility. PLEASE HELP

good point about blocking doesn't cause a creature to tap... that settles it for me. thanks

so using Horseshoe Crab with Hermetic Study, would be an ability used outside of the combat phase, however you can tap and untap it durring the same turn as long as you have enough mana to generate the combo?

that sounds a little more like the intended scope of the card, rathar than endless loops of attacking or blocking during the combat phase.
thanks for your help man. 

ah, thanks for the reference/source