Self-Defense on the Sabbath

Source: H. Graetz, History of the Jews, volume II (Philadelphia: Jewish Publication Society of America, 1893) 2.

This isn't on my reading list, but I don't care because I've wanted to read Graetz's history for a long time--ever since I learned about it in Herman Wouk's classic book on Judaism, This Is My God. Wouk calls Graetz's work a "banquet."

Here's a line the jumped out to me:

"The fact is, however, that Hyrcanus withdrew without accomplishing his siege. It may have been the Sabbatical year which prevented him from proceeding with the siege..."

The context concerns Ptolemy ben Habeb, the brother-in-law of Hyrcanus who killed his (Hyrcanus') father and wanted to take Hyrcanus' life as well. This occurred in the second half of the second century B.C.E. Graetz is unsure about why Hyrcanus stopped his siege of Ptolemy ben Habeb, so he offers the Sabbatical year as one explanation, and the arrival of Ptolemy's Syrian friends as another.

But why would the Sabbatical year have stopped the siege? Hyrcanus was trying to protect his own life, right? Isn't that acceptable on the Sabbath? In I Maccabees 2:32-41, we see that the Maccabees allowed Jews to fight on the Sabbath rather than allowing themselves to be killed. Why wouldn't that apply to the Sabbatical year?