Do you then replace the lasting injury roll with a 50% chance of being Captured? That seems extremely strong.That's a good point. The way I'd interpret it is: you can capture a single fighter via takedown in addition to any captured via the serious injury chart.
On the other hand, using it to replace the roll once someone rolls a Captured lasting injury from its normal 50% roll (3 or less) to instead a 50% roll (4 or more) seems ... extremely weak.
Or do you treat it like Webbed, and give a bonus to the roll resulting from Captured?
Best see what your Arbitrator suggests on this one, rather than just the opinion of any of us here, including me.