What is the meaning of "Yad Derech Metzapeh"?
Rashi: He was by the road, looking [Radak - to see who is coming from the war].
Why is "Yad" written "Yach"?
Radak: Eli's heart was beating him and fearful for Aron ha'Elokim that had left. This is like "va'Yach Lev David Oso" (24:6). It is pronounced Yad, i.e. a place - "v'Yad Tihyeh Lecha" (Devarim 23:13).
Why does it say twice that he came, and interrupts in the middle to say that Eli was sitting and looking?
Malbim (13): This comes to explain why he told the city before telling Eli, the Nasi of his nation. It was proper to tell him first! The verse tells that Eli was outside the city, rather, in the gate, on the other side near the road. The herald came from the other side. Therefore, he told the city first.