Reason for Bank Nifty rise today

I have gone through news portals but couldnt understand why did BN rise by ~8 percent today.Can anyone enlighten me on this.

Short covering for this month expiry.

But does every expiry (considering short covering) see this much increase in % terms.? or is this something unusual this time.

Short covering + dow up 3% + underperformance of BN earlier

P.S.: Events happen and reasons follow. IF BN was down 8%, people would have found another set of reasons.