Tennis experts cite her mental toughness , the completeness and variety of her game , her footspeed and footwork , and her one-handed backhand -LRB- which PERSON@1 has described as the best single-handed backhand in the women 's or men 's game -RRB- as the principal reasons for her success .

Her mental toughness and her one-handed backhand are reasons for her success in tennis .
