While recognised investment exchanges sometimes halt trading or very occasionally cancel transactions, for example as a non-regulatory circuit breaker, or when trades, known as “fat finger” trades, are placed in error, it is very rare for them to suspend trading for days, or to cancel entire trading sessions. Yet, that is what happened earlier this year at the London Metal Exchange (LME). This article considers US activist hedge fund Elliott Management’s challenge of the LME’s decision to cancel trades.