Besides being dismounted with a lance stroke a man could be wrestled out of the saddle, as described by the Monk of St Denis in his account of the de Carrouges vs. le Gris duel in 1386. "With his left hand he seized the top of his opponent’s helmet, and drew Jacques toward him and then pulling back a little, threw Jacques to the ground where he lay weighed down by his armor. Jean then drew his sword and killed his enemy, though with great difficulty, because he was fully armored."
William Rishanger reports the encounter between the future Edward I and the count of Chalons at a tournament that got out of hand, the 'little battle of Chalons' in 1273.
The count penetrated Edward's formation and came very close to him, and finally cast aside his sword, and put his arm around Edward's neck, and gripped him with all his strength and tried to pull him from his horse. But Edward held himself stiffly upright, and when he felt the count gripping him firmly he put his spurs to his horse and pulled the count out of his saddle, so that he was hanging from his neck, and vigorously shook him off and cast him down to the ground.
Rishanger, William, and Henry T. Riley. 1865. Willelmi Rishanger, quondam monachi S. Albani, et quorundam anonymorum, chronica et annales, regnantibus Henrico Tertio et Edwardo Primo. London: Longman, Green, Longman, Roberts, and Green. pp. 79-80 Translation copyright Will McLean 2012