Roman pikeman and spearman

[Ilya Litsios]

He also calls the position of the second-third and four rankers "εἰς ἀκοντισμὸν προβεβλήσθων τοὺς κοντοὺς"

It may mean "as for throwing" or "for throwing".

It's very doubtful that Arrian would use in his instruction the same technical word for two different actions: throwing and stabbing (and "stabbing" is, at least, a very unusual meaning here).
By the way, when Maurice in his Strategicon gives his version of Arrian's anti-cavalry formation, he says that: "The first, second and third man in each file form a foulkon, interlocking their shields, fix their spears [kontaria] firmly in the ground, holding them inclined forward and straight outside their shields... The third man... and the fourth man hold their spears like javelins so when the foe gets close they can use them either for thrusting or for throwing and then draw their swords." When Maurice's infantry fights against infantry, then all four ranks should throw their spears and draw swords.