There are several possibilities to configure a Raspberry Pi to be "a man in the middle" (a very common hacking issue). Because I don't know what do you exactly want to achieve, I will show a simple configuration with a bridge. This is completely transparent to the PS4 but you are able to monitor any traffic of it.
Of course you need an additional USB to wired ethernet dongle because the RPi 3B+ has only one wired ethernet port. If you have plugged it in then with
ip link show you will find it with interface name eth1. The built-in interface is named eth0. Now we can use systemd-networkd to build a bridge. I assume you are headless with your RasPi, means you do not have a monitor and keyboard attached to it. So you have ssh enabled and are logged in with it to the RasPi. First activate systemd-networkd. You have to be very careful because you have only one try. If you make a mistake/typo, then you cannot ssh into the RasPi again after reboot and you have to use a monitor/keyboard or start over again with a fresh flashed image.
# disable classic networking
rpi ~$ sudo -Es
rpi ~# systemctl mask networking.service
rpi ~# systemctl mask dhcpcd.service
rpi ~# mv /etc/network/interfaces /etc/network/interfaces~
rpi ~# sed -i '1i resolvconf=NO' /etc/resolvconf.conf
# enable systemd-networkd
rpi ~# systemctl enable systemd-networkd.service
rpi ~# systemctl enable systemd-resolved.service
rpi ~# ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf
Then setup the interfaces with this three files:
rpi ~# cat > /etc/systemd/network/02-br0.netdev <<EOF
rpi ~# cat > /etc/systemd/network/04-br0_add-eth.network <<EOF
rpi ~# cat > /etc/systemd/network/12-br0_up.network <<EOF
Double check your setup, you have only one try. Then Reboot and ssh into the RasPi again. Please note that the RasPi has very likely got a new ip address because the interface has changed to br0.
Now with tcpdump you can monitor the traffic of the PS4. Install it with
rpi ~$ sudo apt install tcpdump
Look at the raw traffic of the PS4, assuming it has the ip address 192.168.50.170:
rpi ~$ sudo tcpdump -Ai br0 host 192.168.50.170
For example here a snippet from captured data:
14:00:06.989081 IP lga34s11-in-f14.1e100.net.http > 192.168.50.170.42754: Flags [P.], seq 1:529, ack 75, win 236, options [nop,nop,TS val 1124648216 ecr 3263002954], length 528: HTTP: HTTP/1.1 301 Moved Permanently
C....}yJHTTP/1.1 301 Moved Permanently
Content-Type: text/html; charset=UTF-8
Date: Wed, 05 Jun 2019 13:00:06 GMT
Expires: Fri, 05 Jul 2019 13:00:06 GMT
Cache-Control: public, max-age=2592000
<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
The document has moved
Of course this are the raw data from an IP packet but even a newbie can see that google is telling the PS4 that the document has moved and that you have to look at http://www.google.com/. The PS4 has tried to GET http://google.com/.