Why does it say that Sha'ul captured the kingship?k
Radak: He solidified the kingship without any objections. All Yisrael saw that he succeeded in his wars.
Malbim: As long as Pelishtim ruled over Yisrael, his kingship was not so strong.
What is the meaning of "uv'Chol Asher Yifneh Yarshi'a"?
Rashi (Eruvin 53b): He did not rule according to the Halachah. 1
Bamidbar Rabah 11:3: He defeated [the enemy], due to his merits. He ate Chulin in Taharah, spent his money liberally but was concerned for others' money, he equated his slave's honor to his own, and the merit of Torah.
Midrash ha'Gadol (Bereishis 49:27): Initially, he was like a one-year old (without sin). After becoming king, uv'Chol Asher Yifneh Yarshi'a (he did evil).
Radak: He terrified and befuddled [the enemy]. The same applies to "v'Hu Yashkit u'Mi Yarshi'a" (Iyov 34:29).
Me'iri (Eruvin 53b): He did not tell Talmidim in advance what he will teach. As a result, they could not answer properly, and he established them to be Resha'im 2 and ignoramuses.
Malbim: [Sha'ul fought and defeated] anyone who wanted to do evil to Yisrael.
53b: David was Gali Masechta. (taught to others. Alternatively, he explained teachings to understand them well.) It says about him (Tehilim 119:74) "Yere'echa Yir'uni v'Yismechu" (people will delight, for he obtains the correct Halachah). Sha'ul was not Gali Masechta - "uv'Chol Asher Yifneh Yarshi'a". Gaon Yakov - even though the verse teaches his attribute (refer to 14:47:2:2), we expound so, since it did not say Yatzli'ach or Yaskil. Heaven forbid to say that usually, "Bechir Hashem" did not rule like the Halachah! It was only once, regarding Amalek (and killing Kohanei Nov resulted from that).
Granted, due to this they seemed to be ignoramuses. Why did he establish them to be Resha'im? Maharsha (Sanhedrin 93b) - Rasha (or Yarshi'a) refers to transgressing Torah law (in this case, because they err. Shegagah of learning is considered Mezid - Avos 4:13). (PF)
