The pointed pick struck Trotsky’s skull, punching through his parietal bone and penetrating almost three inches into his brain. Trotsky let out [a] long, mournful cry [that Mercader never forgot]. Despite his injury, he fought back. He spat in Mercader’s face and began struggling with him, biting his hand. The sixty‐year‐old Trotsky put up such a fight [that] he broke Mercader’s hand, and the commotion drew Trotsky’s bodyguards. Bursting into the room they latched onto Mercader and started to beat him savagely. Only Trotsky’s intervention saved him.

“No … don’t … kill … him.” Trotsky labored to speak. “We… need … answers.” The men did as he said and restrained the bruised and bleeding assassin.

(Source.)

Also when his bodyguards came in, he told them not to kill the assassin because they needed him to talk

The climate in Mexico varies significantly with its topography. Although much of Mexico contains arid deserts and tropical environments, mountaineering is practiced, particularly on the high-altitude volcanoes in the inner part of the country, some of which are within 60 miles of Mexico City. These volcanoes are crowned with snow and ice and require appropriate mountaineering equipment (e.g. ice axes) for successful ascents. While it is possible that Ramon Mercader chose an ice axe to assassinate Trotsky because he was a mountaineer, owned the object, and was skilled in its use, no evidence of his participation in this alpine activity has surfaced. Rather, Mercader’s association with the Soviet security apparatus may shed light on his choice of weapon for the assassination.

(Source.)