Question: What sport are Mary-Ann Eisel and Christo van Rensburg known for playing?

Context paragraphs:
1989 Paris Open – Doubles: Paul Annacone and John Fitzgerald were the defending champions but they competed with different partners that year, Annacone with Christo van Rensburg and Fitzgerald with Anders Järryd.

1995 Tel Aviv Open – Doubles: Lan Bale and John-Laffnie de Jager were the defending champions, but did not participate together this year.  Bale partnered Wayne Black, losing in the semifinals.  de Jager partnered Christo van Rensburg, losing in the first round.

1985 Australian Open – Men's Doubles: The Men's Doubles tournament at the 1985 Australian Open was held from 25 November through 8 December 1985 on the outdoor grass courts at the Kooyong Stadium in Melbourne, Australia.  Paul Annacone and Christo van Rensburg won the title, defeating Mark Edmondson and Kim Warwick in the final.

Mary-Ann Eisel: Mary–Ann Eisel (born November 25, 1946) is an American former tennis player.  She was the US Open mixed doubles champion in 1968.

1991 Riklis Classic – Doubles: Nduka Odizor and Christo van Rensburg were the defending champions, but did not participate together this year.  Odizor partnered Bryan Shelton, losing in the semifinals.  van Rensburg partnered John-Laffnie de Jager, losing in the first round.

Christo van Rensburg: Christo van Rensburg (born 23 October 1962) is a former professional tennis player from South Africa.

1987 Australian Open – Men's Doubles: Paul Annacone and Christo van Rensburg were the defending champions, but lost in the semifinals to Swedes and top seeds Stefan Edberg and Anders Järryd.

1990 Volvo U.S. National Indoor – Doubles: Paul Annacone and Christo van Rensburg were the defending champions.  Annacone competed alongside Kelly Evernden but lost in the semifinals, while van Rensburg played with Kevin Curren and lost in the quarterfinals. <br>Darren Cahill and Mark Kratzmann won the title, defeating Udo Riglewski and Michael Stich 7–5, 6–2, in the final.

1993 Open 13 – Doubles: Arnaud Boetsch and Olivier Delaître won the title, defeating Ivan Lendl and Christo van Rensburg 6–3, 7–6 in the final.

1990 Ebel U.S. Pro Indoor – Doubles: Paul Annacone and Christo van Rensburg were the defending champions.  Annacone participated with John Fitzgerald, and lost in the quarterfinals to Scott Davis and David Pate, while Van Rensburg played with Kevin Curren, and lost in the semifinals to Grant Connell and Glenn Michibata. <br>Rick Leach and Jim Pugh defeated Connell and Michibata 3–6, 6–4, 6–2, in the final.

Supporting paragraphs: Mary-Ann Eisel Christo van Rensburg
Answer: tennis player