Intent has nothing to do with the rule. Depending on the situation and the ref it may come into play, but accidental obstruction is still obstruction, like Nicky pointed out it may not be the fault of the first person but when his teammate uses him as a sheild the obstruction takes place.

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An aquifer is a water bearing layer of rock or soil. Aquifers are separated by impermeable layers of rock or clay called an aquitard. Aquitard, however may sound a bit offensive to some, and therefore we will be changing the name to Aquachallenge.