Template:M summ Equity Derivatives 6.3(b)
Relevant for Market Disruption Events. Where your Transaction is an Index Transaction or an Index Basket Transaction, the disruption relates to trading on Exchange for at least 20% of the Shares comprising the Index — because the Index doesn’t exist 'per se' as an independently investable security, though it may do as an exchange traded derivative.
Index Adjustment Events
There are separate disruption events relating to change, cancellation or non-publication of Indices. For that see Section 11.1(b) relating to Index Adjustment Events.