Was the threat of a good "patz" from one patriotic granny in her 90s perhaps the motivation for Springbok coach Rassie Erasmus to get his substitutions strategy perfect in the Rugby World Cup?A heartwarming letter shared on the popular Facebook group #ImStaying might prove to hold the clue.While Erasmus' use of substitutions has been hailed by rugby analysts as a major factor in the Springboks' victorious World Cup campaign, it was widely questioned last year after a match which the Boks narrowly lost to the then reigning world champions and bitter South African rivals, New Zealand.On Sunday, Julia Markus shared a letter on the group which her rugby-mad granny, now 93, sent to Erasmus last year."I know the RWC has come and gone, but I wanted to share the following. My grandmother is 93 years old. She will be 94 in March. I like to think she is one of the oldest, if not biggest Springboks supporter. When we won, she watched the highlights on repeat x3 times! (Didn't we all)," Markus posted.The letter reads as follows: "Dear Mr. Erasmus"Mazaltov [congratulations] to you and your team! You have done wonders with the Springboks. I have watched rugby since the 1940s - walked all the way from the top of Oranjezight and caught the train to Newlands rugby ground every Saturday."I watched Okie Geffen, James Small and all the super rugby commentators on TV. I am aged in the 90s and nearly landed in the Pinelands cemetery on Saturday. How the HECK could you change your perfect team, 10 minutes before the end against New Zealand - you know they always win in the second half. DON'T YOU EVER DO THAT AGAIN! - I would come and give you a good patz (hiding) if I was your mother. However, all forgiven!"Lots and lots of good luck for the next four games overseas. If I am not here for the World Cup and we win, I'll send you a postcard from above. Totsiens en alles van die beste (Goodbye and best wishes)."PS. Ek is 'n ou Namaqualander (I'm an old Namaqualander)."While it is unclear if the letter ever reached Erasmus, the post was well received on Facebook.It had been liked nearly 3 000 times, and been shared more than 150 times by 14:30 on Monday. Among those who commented is the mother of late Springbok wing and 1995 World Cup winner, James Small."James would have been humble, but would have loved the special mention. Salute you Mam," Vourn Small responded to the post.Several of the people who commented suggested that Erasmus and the Boks pay her a visit.