Daniel Brettig is an assistant editor at ESPNcricinfo. @danbrettig
Steven Smith was ruled out of the Lord's Ashes Test and was highly unlikely to take the field in the next Test at Headingley after he became the first cricketer to be formally substituted out of a Test match with concussion, replaced on the final day of the match by Marnus Labuschagne.
While Smith had initially passed concussion testing and returned to complete his innings in the hour after he was struck a sickening blow to the neck by Jofra Archer on the fourth afternoon, mandatory subsequent testing on the fifth morning of the match revealed his condition to have deteriorated.
On the official notification by the Australian team to the ICC match referee Ranjan Madugalle, Smith's symptoms were described as "headache, dizziness, feeling slowed down, feeling in a fog, don't feel right, drowsiness". He is set to undergo further precautionary scans on his neck to assess whether there is any further damage.
"As part of the Cricket Australia concussion protocol, repeat concussion testing of Steve Smith was also performed this morning and demonstrated some deterioration from his testing which is consistent with the emergence of the symptoms he was reporting," a Cricket Australia spokesman said. "On that basis Steve has been withdrawn from the match by team doctor Richard Saw and the Australia team will lodge an application for a concussion substitute with the ICC match referee in line with the ICC protocol.
"Cricket Australia statistics show that 30 percent of concussions in Australian cricket are delayed. It is not uncommon for players to pass their tests and feel well on the day of an injury and then display symptoms 24 - 48 hours later. In terms of Steve's availability for the third Test, this will be considered over the coming days but the short turnaround to the next Test is not in his favour. Steve's fitness will be assessed on an ongoing basis.
"Steve will undergo a precautionary scan on his neck on Sunday. Despite the unfortunate nature of what has happened, the positive is that the concussion protocol, including the availability of the concussion substitute, which has been recently brought in has served its purpose. A player is no longer under pressure to take the field when he or she displays symptoms of concussion and a side is not disadvantaged having lost a player to a blow to the head or neck."
Each of the ICC, CA and the ECB have their own concussion policies, but all stress the need for caution in dealing with potential or actual concussion cases. CA's policy, which was used in domestic cricket as a forerunner to the introduction of a concussion protocol for international cricket at the start of this Ashes series, states "in case of uncertainty, the qualified medical officer should always adopt a conservative approach to return to play".
The ECB's policy is the strongest in terms of fixing a player's return date: "All symptoms need to be absent for 24 hours before simple cognitive and physical activities can be undertaken. Graded steps of gradual increase in activity must be accompanied by a 24-hour window to check for further symptoms or signs…the player needs a 24-hour window for each level and therefore means no further return to a full training situation for six days."
CA's policy underlines the fact that a graded return to physical activity is required, and if there is any instance of a deterioration or setback then the process must begin again: "Staged physical activity should be upgraded on a graduated basis with progression through stages and Participants must return to a previous stage if symptoms worsen. A Participant may be required to sit out the duration of a multi-day match and/or further matches if required through the medical review."
Lastly, the ICC's guidelines make a similar statement but also add that a typical recovery process will take about seven days to complete. The third Ashes Test at Headingley is scheduled to begin on Thursday, as the second of back to back Tests. "If at any of these stages symptoms return the player should drop back an exercise level," ICC guidelines state. "If the player is a student they may require a couple of days off school to rest.
"A player should not return to full training if unable to attend school or work without symptoms returning. A concussed player requires a formal medical clearance to return to training and play and never permitted to return on the day of the injury. Usually a player will recover in about seven days but this can vary from individual to individual."