A rugby player's value to his or her team is best measured by the impact of their absence.
Franco Mostert is one such player. The lock is one of the Springboks' more understated players, a guy who goes through a Test match relatively unnoticed, but he is someone who shines in absence when he is not available to play in the green-and-gold jersey.
Mostert didn't feature in three Test matches for the Springboks in 2018, including the one-off fixture against Wales in Washington D.C. in June because he was rested for the England series. He also missed the Rugby Championship match against Argentina in Durban, when he was injured, and the first November tour match against England, which was played outside the Test window.
The Boks won all 10 of their lineouts against Wales, and two of the Dragons', but the set piece subsequently malfunctioned at crucial times when they were on attack in the opposition half against Argentina and England.
The Boks lost three out of 18 lineouts against Argentina in Durban and four out 18 against England at Twickenham with Eben Etzebeth and Pieter-Steph du Toit in the second row. South Africa managed to beat the Pumas, but they lost to England by a single point.
Mostert, who recently joined Gallagher Premiership club Gloucester, returned to action for the Test against France, which saw the Boks win 16 out of 16 lineouts on their own throw.
It's obviously unfair to give Mostert all the credit for the improved showing in this set piece, as hookers Malcolm Marx, especially, and Bongi Mbonambi were much-improved from previous weeks. But Mostert seems to bring a calmness to the Boks lineout, because of his skill in the air and his calling.
When Marx was struggling to find his jumpers in the middle and the back of the Boks' lineout, a call should have been made to rather throw to the front, which is a much safer ball but obviously a lot harder to maul from or to attack from if the ball is to be played off the top.
Mostert called the ball on himself in the middle when Mbonambi had to feed a lineout long after the hooter had sounded with the Boks trailing in Paris. The lineout was executed to perfection, and the Mbonambi scored the winning try from the resulting maul.
Lineouts have actually been key over the two weekends during the November Tests. The set-piece had a massive influence in the Springboks' match against England, and it was also one of the factors that helped the All Blacks beat Eddie Jones' men in London the following week.
England's lineout dominated in the first half against the All Blacks, which enabled them to get their driving maul going and led to a try in the first half. However, All Blacks coach Steve Hansen countered this by replacing flank Liam Squire with lock Scott Barrett, who went to the front of the lineout to contest England's ball.
The home side ended up losing five lineouts, including surrendering the ball in a few good attacking positions.
There are a lot more lineouts than scrums in matches -- on average more than double during the last two weeks - so the ability to secure good ball at this set piece has become vital both in controlling where the match is played and as an attacking platform.
The Springboks' lineout seems to be a 50 percent more efficient when Mostert is in the No. 5 jersey, while Etzebeth in front and a du Toit at the tail are also very good options.
The scrum is still a massive part of the game, but a good lineout may just be the key to win the Rugby World Cup in Japan.