I really hope that they don't show them clashing & make it a drama. Bhisma wanted to see the full glory of the lord rushing towards him as Arijit said.
Krishna's & Bhishma's encounter at Kurukshetra is explained in Chapter Nine of the First Canto of Srimad-Bhagavatam:
"In the midst of the great battle, surrounded by the clash of arms, the pounding of hooves, the rattle of trappings, the shouts of warriors, and the screams of wounded men and beasts, where the dust churned up by the horses dimmed the sun and blood turned the earth to mud, Krishna suddenly stopped the chariot and sprang to the ground. Raising the wheel of a disabled chariot over His head, the Lord raced toward the great general Bhishmadeva like a lion charging an elephant. Just moments before, wave after wave of lethal arrows from Bhishmadeva's bow had crashed relentlessly down upon Arjuna's chariot. In amazement, the other warriors had seen the figures of Arjuna and his driver Sri Krishna completely disappears behind the curtains of the general's arrows.
And then Bhishmadeva's bow was still. It dropped to the ground, and the invincible general stood unarmed and stared with widening eyes at the Lord charging furiously toward him. In intense concentration he noted every detail of Krishna's appearance: He saw how the beautiful flowing black hair of the Lord had turned ashen from the dust of battle; he saw how beads of sweat adorned His face like dew on a blue lotus flower; he saw how red smears of blood from wounds made by his own arrows enhanced the beauty of the transcendental body of the Lord. Bhishmadeva watched the Lord rushing toward him, preparing to kill him with a hurl of the wheel, and he was filled with ecstasy."
This encounter on the battlefield between Lord Krishna and Bhishmadeva was not the hostile clash of enemies that it appears to be. On the contrary, it was the reciprocation of deepest love between the Supreme Personality of Godhead and one of His great devotees, and from it both derived the highest transcendental bliss.
It is a pity that the SP has not shown any kind of devotion to Krishna that Bheeshma had whereas in reality the grand old man was one of his pure devotees.