Hello Krish I think this "beat up" is "beat-up", an adjective, which means "damaged", "worn out", etc.. The sentence could be rephrased as "She is afraid she would get beat-up if/when she runs around these tunnels". What I can't get is why the writer pluralizes "tunnel" as "tunnels" despite the fact that s/he writes "There is an entrance" in the preceding sentence.
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