(لَوْ يَجِدُونَ…) (If they could find…): When these battles occur, if only they could find:

…مَلْجَأً..  (a refuge): It is a place he could hide in to protect himself from harm.

…أَوْ مَغَارَاتٍ…  (or some caves,): This is like a cavity or a hollow in the mountain.

…أَوْ مُدَّخَلًا…  (or any place to enter [and hide]): It is like an underground tunnel that you enter through a twisting path.

So, during the battle, the hypocrite tries to take refuge in a shelter or enters a cave or a hiding place so he can protect himself from the fighting and distance himself from danger.

…لَّوَلَّوْا إِلَيْهِ وَهُمْ يَجْمَحُونَ  (they would turn to it while they run heedlessly.): They would run to it at an extremely fast pace, without control over themselves, due to their fear and the anxiety that overwhelms them in these battles. It’s like saying, “The horses run heedlessly,” meaning they went out of control.