Pinning happens at stock option expiry when market makers push...

Pinning happens at stock option expiry when market makers push the stock near an option strike

Have a look at where BHP expired yesterday. Anyone who had $20 puts or calls could have been forced into action to close positions because of the chance they would have been assigned or exercised. Market makers usually widen the spread on those $20 puts and calls at that time and they make some easy money