p4: "Just what is thinking Aikawa" (probably "Just what is Aikawa thinking?")
also p4: ヘディング is a football/soccer term: header. Right now it's a bit homoerotic (Kappa).
Yes, the word order is at best anastrophic. But an “of” or “about” would change the meaning. “What are you thinking?” questions the general nature of the thought and idiomatically challenges the soundness of the thought; “About what are you thinking?” simply asks about the focus of concern.
@Levanah Above all, it doesn't look out of place. They are, after all, mere children. In typical shounen when a high schooler is so clueless for 100 chapters, it's getting a bit too far-fetched.