Mumbai Indians’ (MI) clash against Chennai Super Kings (CSK) on Thursday (April 23) produced an unusual moment on the cricket field that quickly became a talking point.

In the 17th over, Mitchell Santner completed a sharp low catch to dismiss Sanju Samson but landed awkwardly, appearing to injure his left shoulder. He walked off in visible discomfort, with his arm later seen heavily iced and supported in a sling. However, Mumbai Indians opted for a concussion substitute, bringing in Shardul Thakur for the second innings, prompting questions over how the decision aligned with IPL rules.

Concussion call despite visible shoulder injury

The confusion largely stemmed from the visible nature of Santner’s injury. While it appeared to be a shoulder issue, head coach Mahela Jayawardene clarified that the concern extended beyond what was immediately evident.

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“Santner hit his head first, then the neck, and obviously the shoulder as well. Once he got back to the dressing room, he felt unstable and complained of dizziness. While the ice was for the shoulder, the concussion protocol took precedence because he failed the initial balance test.”

Under IPL regulations, a team is not required to prove a confirmed concussion. A diagnosis of “suspected concussion” by the team doctor is sufficient to trigger the substitution protocol. Based on that assessment, the match referee approved Mumbai Indians’ request.

‘Like-for-like’ rule sparks debate

The second point of debate centred on whether Shardul Thakur qualified as a like-for-like replacement for Santner. IPL rules mandate that a concussion substitute must be broadly similar in role to avoid giving a team an undue advantage.

Santner, a left-arm spin-bowling all-rounder, was replaced by Thakur, a right-arm pace-bowling all-rounder. The match referee cleared the substitution on the basis that both players fall under the all-rounder category.

Have a look at some of the reactions below:

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There was also speculation around a “Serious injury replacement” rule, but while such a provision exists in domestic multi-day cricket, it has not been implemented in the IPL. At present, concussion substitutes remain the only in-match replacements permitted to both bat and bowl.

Despite the debate, the move had little impact on the outcome. Mumbai Indians were bowled out for 104, suffering a 103-run defeat, with Thakur contributing 6 runs off 12 balls.