CSK thrash MI but concussion substitute controversy at Wankhede steals the spotlight; what do the rules say?

It was a merry night for the Chennai Super Kings as they brought down the Mumbai Indians in their own backyard. On Thursday, CSK invaded the fortress of Wankhede Stadium and sealed a hammering 103-run win over arch-rivals as yellow became the colour of the evening.

Despite not having stars like Ayush Mhatre and Khaleel Ahmed, CSK pushed through in the competition and delivered a splendid all-around performance as MI were handed their biggest-ever defeat in the IPL.

While the IPL's El Clásico delivered the entertainment it promised, a controversial moment erupted during the action when Shardul Thakur walked in as the concussion substitute.

MI's Shardul replaces Santner, creates controversy

In the 17th over, Mitchell Santner hurt his shoulder while completing a catch to dismiss Kartik Sharma during the first innings. The Kiwi cricketer looked in pain and had to walk off the field.

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The New Zealand T20I skipper had completed his four-over spell, picking up Sarfaraz Khan's wicket and conceding 44 runs.

But what's interesting was that Shardul Thakur, who wasn't in the Playing XI, replaced Mitchell Santner during the Mumbai Indians' chase as concussion sub. He walked out to bat at the number eight spot for MI, scoring six off 12 deliveries before being dismissed by Anshul Kamboj.

What does the IPL's rulebok states?

The video replay showed Mitchell Santner hitting his head during the catch attempt, triggering the concussion protocol, allowing a substitute to enter the game.

As per the IPL's regulations, concussion substitutes are only allowed when there is a confirmed or suspected concussion. A like-for-like replacement is required for the same, and the match referee has to approve it.

While the rule is within the IPL's framework of rules, the situation sparked a huge chatter over the decision on social media, with fans calling out the grey areas of a suspected concussion.

Given the grey areas in the substitution rules, the decision to allow a full replacement has come under scrutiny