Final answer:
Hamlet fights with Laertes at Ophelia's funeral to show that his own grief is greater, highlighting the themes of madness and sincerity of grief in Shakespeare's play.
Step-by-step explanation:
The altercation between Hamlet and Laertes at Ophelia's funeral stems from Hamlet's desire to demonstrate that his grief for Ophelia surpasses that of Laertes. Overcome by emotion and fraught with a tumultuous mix of sadness, regret, and anger, Hamlet leaps into Ophelia's grave after watching Laertes express his own loud grief. Their clash is not over murder nor a direct challenge by Laertes, but rather out of a profound sense of loss and a competition of sorrow, which reveals the deep complexities of Hamlet's character and furthers the theme of madness and authenticity of grief that pervades the play.