וַעֲשִׂיתֶ֕ם בְּי֥וֹם הֲנִֽיפְכֶ֖ם אֶת־הָעֹ֑מֶר כֶּ֣בֶשׂ תָּמִ֧ים בֶּן־שְׁנָת֛וֹ לְעֹלָ֖ה לַיהוָֽה׃
И в тот день, когда вы будете махать снопом, вы принесете агнца без порока первого года всесожжения Господу.
Rashi
ועשיתם... כבש AND YE SHALL OFFER… A LAMB — This came (was brought) as an obligatory sacrifice in connection with the Omer.
Ibn Ezra
The Dissenters claim that yearling does not mean “a year old” [cf. comment on 12:6]. The former, according to them, denotes an animal under one year of age, whereas the latter denotes an animal one year old or older. The passage dealing with the dedication of the Altar, however, speaks of “one yearling lamb” [Numbers 7:15], yet in the end gives a total count of “twelve one-year lambs” [Numbers 7:87].
Siftei Chakhamim
An obligation in connection with the omer. Rashi is answering the question: Why in parshas Pinchas (Bamidbar 28,) which lists [all] the additional offerings [of Pesach], as Rashi explains (in verse 8), is there no mention of this sheep? He answers: This sheep is not brought as an additional offering but comes as an obligation in connection related towith the omer.