Real Madrid's Cristiano Ronaldo (white 7) races forward with the ball and does his trademark "skip" to simultaneously change direction of the ball and himself. Subsequently, the defender (red 2) tries to adjust himself accordingly. Here are the freeze frames:
Clash of thighs and knees here!
Full impact of downward force on left leg (red player)
Unfortunately, there was slight contact as the Celta Vigo defender's left knee brushed against Ronaldo's right thigh just before he expected to land on his left foot and push off hard to change his direction. At high speed, this alters certain trajectories of movement, so that now the defender's left leg has a more open (obtuse) angle than anticipated which cannot take the full impact of the downward force exerted on it. The left knee jarred and crumpled (plus the ankle may have also been sprained) and this is why the freak injury occurred.
Furthermore, Ronaldo's right leg trajectory was also altered, which is why he lost his footing and fell.
A freak injury caused by unexpected minor contact
Why post about this? In the EPL, there is much heated discussion about Tottenham Hotspur player Gareth Bale and his reputation for diving or going to ground easily. He has been cautioned five times since the beginning of the season, all for simulation. Some of his cautions were correct and some are debatable because there was contact before Bale went to ground.
This concept of "slight contact" having a significant effect on an athlete moving at high speed perhaps deserves more consideration. Match officials are always striving to improve their skills, and having more examples and research on this concept can help Referees better understand why some players may appear to go down easily at the slightest contact. Can slight contact really have a major impact on a player's movement? Further examples and research would benefit Referees who encounter such incidents at the highest (and fastest) levels.
Sunderland 1 Tottenham 2: Bale caught up in new diving storm but Spurs go marching on (Daily Mail)
Bale dives into face-to-face talks with ref Marriner as Spurs ace tries to get rid of his reputation (Daily Mail)