Thread by @Scienceofsport

Let's talk about foul play, red cards and head injuries in #Rugby Here's a thread on head injury risks and the 'levers of control' to try to reduce it, with some background and some data... 1/

Back in 2017, when we first analysed risk factors for head injury, it was clear that higher tackles increased risk. This is pretty obvious - the only way a ball carrier can be injured is from a high tackle, and we also found head-to-head contact was most dangerous for TACKLERS

This was the trigger or catalyst for a clampdown on high tackles. This would DIRECTLY protect the ball carrier, but harsher sanctions, applied more frequently, would carry a MESSAGE to tacklers to target lower, and avoid those highest risk head contact situations

Back then, 6% of all head injuries happened in what were called "illegal tackles", which were penalized, either with a penalty, or yellow, or red card. So 1 in 16 head injuries were the result of foul play. Let's now look at the situation as it is in 2022. Brace yourselves...

In the PRL and Super Rugby in 2022, 25% of all head injuries happen in foul play tackles. The risk of a head injury in a tackle that is red carded is 232 times higher than in a legal tackle. Yep, 232 times higher head injury risk when the tackle is judged as a red card by the ref

Put differently, it means that:
Every 1.7th red carded tackle causes a head injury;
Every 4.7th yellow carded tackle causes a head injury;
Every 19th penalized tackle causes a head injury;
Every 395th legal tackle causes a head injury (needing HIA)
So that's 232x more risk for RC

Here's a different graph of the same dataset, showing the propensity (how many HIAs per 1000 of each event type) for legal tackles, penalties, yellow cards and red cards. The pattern is "comforting" because sanction & danger rise together.

Now, remember, that there is a Head Contact Process to guide these sanction decisions. We can use that (as we should) to define a red card as "A tackle that involves direct head contact, that is high in danger, and lacks any mitigation", as you can trace below.

Now take these two things together. What the data is saying is that "A tackle that involves direct head contact, that is high in danger, and lacks any mitigation" is 232 times more likely to result in a head injury that a legal tackle, that is not sanctioned. If risk is lower, YC

You may be wondering where the risk lies between the tackler & the ball carrier for these illegal tackles. Well, obviously, MOST of the risk increase is for the ball carrier, when tackles are illegal. This graph is specific for HIAs to the ball carrier in tackles. 778x more risk!

But, and this is a key point, the tackler is ALSO at elevated risk when committing an illegal tackle, as this graph shows. 37x more chance that the tackler suffers an HIA when making a tackle that is red carded, compared to legal. Illegal tackles create risk for BOTH players!

The fact that 25% of head injuries (it's 49% of ball carrier head injuries and 9% of tackler head injuries, btw) happen as a result of illegal tackles is very powerful. It used to be 6%, but that's gone up because more tackles are now sanctioned than used to be the case.

The magnitudes of risk increase (hundred fold or more) is also by far the largest for any factor we look at - speed, height, tackle type, direction etc all affect risk, but nothing comes close to the risk increased caused by an illegal tackle. It's a lever that can't be ignored

So I know as fans we hate seeing red cards. But you're seeing an action that is 778x more likely to injure a ball carrier, 232x more likely to injure either player, and 37x more likely to injure a tackler making that tackle. And yes, getting this down is really, really difficult

In the above, by the way, a "head injury" is anything requiring an HIA. It may be confirmed as a concussion, or it may not. But it's sufficient for the player to leave the field at the time. And these are so orders of magnitude more likely when the tackle is illegal.