6. In the All-Star basketball game, 27 players participate, each wearing a jersey with their favorite number, which is a non-negative integer. After the game, they line up in a 3-row, 9-column formation for fans to take photos. An eccentric fan only takes photos of the following type: the players in the frame form a rectangle of $a$ rows and $b$ columns $(1 \leqslant a \leqslant 3,1 \leqslant b \leqslant 9)$ (the row and column directions are consistent with the original formation), and the sum of the jersey numbers of the players in the frame (for a single player, it is the player's jersey number) is a multiple of 10. As a result, this fan only takes photos of $s$ players. Find the minimum possible value of $s$.
Prompt: $s_{\text {min }}=2$.
Assume at most one player is photographed.
By symmetry, without loss of generality, assume no players in the first row are photographed.

For $i=1,2, \cdots, 9$, let the players in the $i$-th column of the 1st, 2nd, and 3rd rows have jersey numbers $a_{i}, b_{i}, c_{i}$, respectively, and denote
$$
S_{k}=\sum_{i=1}^{k} a_{i}, T_{k}=\sum_{i=1}^{k}\left(b_{i}+c_{i}\right),
$$

where $k=0,1, \cdots, 9$.
Considering the 1st row, the 2nd to 3rd rows, and the 1st to 3rd rows, respectively, it can be proven that $S_{0}, S_{1}, \cdots, S_{9}, T_{0}, T_{1}, \cdots, T_{9}$, and $S_{0}+T_{0}, S_{1}+T_{1}, \cdots, S_{9}+T_{9}$ all form a complete residue system modulo 10, which will lead to a contradiction.

On the other hand, suppose the players choose the numbers as shown in Table 1. It can be verified that no player with a non-zero number can be photographed. In this scenario, the fan exactly photographs 2 players.