Complex sentence: Ice hockey players will develop calluses on the side of the palm due to the friction of the laces when tying their skates and across the inside of the palm under the fingers due to gripping the hockey stick.
Split into simpler sentences: Ice hockey players will develop calluses on the side of the palm due to the friction of the laces when tying their skates. And across the inside of the palm under the fingers due to gripping the hockey stick.