Yuzvendra Chahal became the first concussion substitute to be named Player of the Match in international cricket as he took three wickets after replacing Ravindra Jadeja at the break between innings. When India batted, Jadeja had rescued them with an unbeaten 44 off 23 to give the bowlers something to bowl at. When Chahal came on to bowl, Australia were 54 for no loss in a chase of 162, but he struck to remove Aaron Finch and Steven Smith in his first two overs. His final analysis of 4-0-25-3 - he returned to dismiss Matthew Wade - earned him the match award.
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Jadeja batted with a hamstring strain, which was apparent and had already put his participation for the rest of the match in doubt, and he then top-edged Mitchell Starc on to his helmet on the second ball of the 20th over. The blow was hard enough to ricochet to backward point, where the catch was dropped. He wasn't given a concussion test on the spot, but it is not unusual for concussion symptoms to show up belatedly.
The ICC officials obviously approved the substitution, based on the advice of India's team doctor that Jadeja was concussed as a consequence of an event on the field and during the match, and that Chahal was a like-for-like replacement for Jadeja.
Australia coach Justin Langer, however, was seen remonstrating with match referee David Boon just before the start of the chase. Finch also stood by during the discussion, but didn't appear to say anything.
At the post-match presentation, Finch said that it wasn't fair to question expert advice, and that was the end of the matter.
The concussion assessment was carried out by India's team doctor and BCCI's anti-doping manager Abhijit Salvi, and their physio Nitin Patel. At the press conference, Sanju Samson said Jadeja was asked how he felt when he came back in. He said he was dizzy. India's captain Virat Kohli said at the post-match presentation that Jadeja was dizzy when he returned, and continued to remain so even after the match.
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"Ravindra Jadeja was hit on the helmet in the final over of the first innings of the first T20I," the BCCI tweeted. "Yuzvendra Chahal will take the field in the 2nd innings as a concussion substitute. Jadeja is currently being assessed by the BCCI Medical Team."
This concussion might put Jadeja in doubt for the rest of the series, because head injuries are required to be dealt with seriously, and players are not rushed back in two days' time, which is when the next match will be played. The ICC protocol says: "Generally, concussion symptoms will settle within two-three days and a player diagnosed with a concussion is ready to return in about a week but, in some individuals, this time might be shorter or longer. Medical oversight, as occurs in elite teams, is essential if a player is to return to play within a week or on a subsequent day of a multi-day match."
Kohli remarked that the concussion substitute rule might have worked to their advantage on the day - having originally dropped Chahal on a surface that gripped - but on another day, India might not have a like-for-like replacement in the squad.
Sidharth Monga is an assistant editor at ESPNcricinfo