。
The arrow stuck in with a thud.
Literal
Arrow [topic-は] gusari-[adverbial-と] stuck-in.
ぐさり is a 擬態語 for the sensation of something sharp stabbing into or piercing flesh/wood — often translated 'with a thud' or 'straight in.' The adverbial と follows the mimetic word, as is typical for the adverbial use of 擬態語. 刺さる is the intransitive 'get stuck in' (vs transitive 刺す 'stab').