Overhedging is a form of speculation.
It means intentionally hedging an amount GREATER THAN the total related risk exposure, for example by the use of a derivative instrument with a principal amount of 200% of the related risk exposure.
The effect of overhedging in this way is to create a new purely speculative position in the derivative instrument.
The size of the new speculative position is equal to the excess of the principal amount hedged, over 100%.
In the case above, the size of the new speculative position is 200% - 100% = 100%.
In other words equal in size to the original exposure being hedged.
The new speculative position is in the opposite direction to the original exposure.