5.
SELECT COUNT(G.ID) AS GOALS, P.FIRSNAME, P.LASTNAME
FROM GOAL G
JOIN MATCH M ON M.ID = G.MATCH_ID
JOIN PLAYER P ON P.ID = G.PLAYER_ID
WHERE YEAR(M.DATE) = 2016
GROUP BY G.PLAYER_ID
ORDER BY GOALS DESC
LIMIT 3

6.
WITH ARBITER_MATCHES AS
(
SELECT COUNT(M.ID) AS MATCHES, A.FIRSTNAME, A.LASTNAME
FROM MATCH M
JOIN ARBITER A ON M.ARBITER_ID = A.ID
WHERE YEAR(M.DATE) = 2016
GROUP BY A.ID
),
MAX_MATCHES AS
(
SELECT MAX(AM.MATCHES) AS MAX_MATCHES
FROM ARBITER_MATCHES AM
)
SELECT AM.*
FROM ARBITER_MATCHES AM
JOIN MAX_MATCHES MM ON MM.MAX_MATCHES = AM.MATCHES