Matfield h ated th e nickname h is fellow players gave him - they called him Kiewiet because of his thin legs.
I can believe there are a few tennis players that meets that description - Sinner and Tsisipas are in that category as well. In the case the thin legs was the reaqson why Matfield's playing weight was so low - he claimed in his book it was between 105 and 108 kgs. That meant he could be easily lifted in line outs and he became a star in that caegory - for the rest he prefers to stand around in the backline - since outside of line-outs tight 5 play was not his forte.